feat: combine github_team_membership resource blocks into one

[vedantthapa]

Combine separate github_team_membership resource blocks for maintainers and members into one. This simplifies making changes when reconciling drift in membership.

Consider the following example, terraform plan suggests an update in-place -

[projects/copilot/FociSolutions/teams]
Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
  ~ update in-place
Terraform will perform the following actions:
  # module.team["copilot-enabled"].github_team_membership.members["yeybr"] will be updated in-place
  ~ resource "github_team_membership" "members" {
        id       = "12815562:yeybr"
      ~ role     = "maintainer" -> "member"
        # (3 unchanged attributes hidden)
    }

However, following the suggestion from the previous plan and moving yeybr from the maintainers to members list, instead results in a destroy + create, like so -

[projects/copilot/FociSolutions/teams]
Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
  + create
  - destroy
Terraform will perform the following actions:
  # module.team["copilot-enabled"].github_team_membership.maintainers["yeybr"] will be created
  + resource "github_team_membership" "maintainers" {
      + etag     = (known after apply)
      + id       = (known after apply)
      + role     = "maintainer"
      + team_id  = "12815562"
      + username = "yeybr"
    }
      # module.team["copilot-enabled"].github_team_membership.members["yeybr"] will be destroyed
  # (because key ["yeybr"] is not in for_each map)
  - resource "github_team_membership" "members" {
      - etag     = "W/\"30d522f7bff4946d257244fb97e69ad8da9049cbea62956e11b739c376d67344\"" -> null
      - id       = "12815562:yeybr" -> null
      - role     = "maintainer" -> null
      - team_id  = "12815562" -> null
      - username = "yeybr" -> null
    }

This is likely due to having separate resource definitions for each role. This PR combines the resource definitions into one via an intermediate local variable to transform the list of maintainers and members, into a single key-value pair of username => role. As a result, any suggestions for update in-place can be resolved by moving users to the right list.

[gemini-code-assist]

Summary of Changes

Hello @vedantthapa, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the Terraform configuration for managing GitHub team memberships. By consolidating the separate resource blocks for maintainers and members into a single, unified resource, the change aims to significantly improve the handling of role updates. This prevents the previous issue where changing a user's role from 'maintainer' to 'member' (or vice-versa) would result in a destructive 'destroy + create' operation, instead enabling more efficient 'update in-place' actions. The modification streamlines membership management and enhances the stability of the Terraform state.

Highlights

• Resource Consolidation: The separate github_team_membership resource blocks for maintainers and members have been combined into a single resource block, github_team_membership.memberships.
• Improved Role Management: A new local variable, memberships, is introduced to transform the lists of maintainers and members into a single map of username => role. This allows for in-place updates when a user's role changes, preventing destroy-and-create cycles.
• Test Updates: The Terraform test configuration (team.tftest.hcl) has been updated to reflect the new consolidated github_team_membership.memberships resource, ensuring tests correctly validate team membership and roles.

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[gemini-code-assist]

Code Review

This pull request refactors the github_team_membership resources to use a single resource block, which is a great improvement. It correctly addresses the issue with Terraform's plan showing destroy+create instead of in-place updates when a member's role changes. The implementation is clean and uses a local variable to merge maintainers and members effectively. I have one suggestion to improve the robustness of the merge logic to prevent potential silent privilege demotion if a user is accidentally listed as both a member and a maintainer.