Changed github action runner to ubuntu 18.04

Author: github-actions[bot]

.github/workflows/build.yml

@@ -6,11 +6,7 @@ on:
 jobs:
   build:
     name: Build
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ ubuntu-latest, macos-latest, windows-latest ]
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-18.04
     if: startsWith(github.event.head_commit.message, 'Releasing version') != true
 
     steps:

.github/workflows/early-access.yml

@@ -8,7 +8,7 @@ jobs:
   earlyaccess:
     name: EarlyAccess
     if: github.repository == 'redis-developer/testcontainers-redis' && startsWith(github.event.head_commit.message, 'Releasing version') != true
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     steps:
       - name: Checkout
         uses: actions/checkout@v2

.github/workflows/release.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   release:
     name: Release
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
         with: