fix(ci): global sccache cache tag + tolerate zero-test filters

[synoet]

Fixes two CI regressions exposed by tooling-only PRs (a PR that only touches xtask, e.g. #4294's cargo-deny port).

1. test fails with "no tests to run" on tooling-only PRs

The nextest package filter narrows an xtask-only change to rdeps(=xtask), which selects zero tests — and nextest's default exits error: no tests to run (exit 4). Add --no-tests=pass so an empty selection is a pass; a tooling change legitimately affects no tests.

2. New branches start with a cold cache

The Namespace cache volume is scoped per branch, and check/test only run on pull_request (never on main), so a fresh branch has no default-branch cache to inherit and recompiles the whole workspace from scratch (~5–6 min).

Pin an explicit sccache-ci cache tag on the check/test runner (runs-on: namespace-profile-linux-rust-ci;overrides.cache-tag=sccache-ci) so every branch reads/writes one global volume — the way the old shared S3 sccache bucket did. sccache entries are content-addressed, so concurrent writers can't corrupt each other; worst case is an occasional miss that recompiles.

Note: the tag's volume is brand-new, so the first run on any branch is still cold — the global-warm payoff kicks in once it's seeded.

Regenerate: cargo x workflows from rust/cloud-storage (--check verifies sync).

🤖 Generated with Claude Code

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: fc387a49-18ab-47db-a15e-12a6281fce2c

📥 Commits

Reviewing files that changed from the base of the PR and between 15e469f and ab07ac2.

📒 Files selected for processing (6)

• .github/actionlint.yaml
• .github/workflows/code_check_cloud_storage.yml
• rust/cloud-storage/tools/xtask/src/workflows/code_check_cloud_storage.rs
• rust/cloud-storage/tools/xtask/src/workflows/runners.rs
• rust/cloud-storage/tools/xtask/src/workflows/scripts/run_tests.sh
• rust/cloud-storage/tools/xtask/src/workflows/vars.rs

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📝 Walkthrough

Summary by CodeRabbit

• Chores

  • Optimized CI/CD pipeline caching configuration for improved build performance across cloud storage workflows.
  • Updated runner configurations to leverage shared cache infrastructure for faster compilation times.

• Bug Fixes

  • Fixed test execution behavior to treat scenarios with zero matching tests as success instead of failure.

Walkthrough

The pull request makes two independent CI changes. First, it introduces a CI_CACHE_TAG constant ("sccache-ci") in vars.rs and a new Runner::with_cache_tag method in runners.rs that formats a runs-on label with an explicit overrides.cache-tag suffix. The check and test jobs in code_check_cloud_storage.rs are updated to use this method, which is reflected in the generated workflow YAML and in the actionlint configuration. Second, --no-tests=pass is added to cargo nextest run in both run_tests.sh and the workflow YAML, changing behavior so that a test filter matching zero tests results in success rather than an error.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title follows conventional commits format (fix:), is under 72 characters (62 chars), and clearly summarizes both main changes: the global sccache cache tag and zero-test filter tolerance.
Description check	✅ Passed	The PR description is directly related to the changeset, detailing the two CI regressions being fixed and explaining the rationale behind the modifications across all changed files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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