Use variables for runs-on settings

See gh-42333

.github/workflows/build-and-deploy-snapshot.yml

@@ -8,7 +8,7 @@ concurrency:
 jobs:
   build-and-deploy-snapshot:
     name: Build and Deploy Snapshot
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_MEDIUM || 'ubuntu-latest' }}
     if: ${{ github.repository == 'spring-projects/spring-boot' }}
     steps:
       - name: Check Out Code

.github/workflows/build-pull-request.yml

@@ -7,7 +7,7 @@ permissions:
 jobs:
   build:
     name: Build Pull Request
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_MEDIUM || 'ubuntu-latest' }}
     if: ${{ github.repository == 'spring-projects/spring-boot' }}
     steps:
       - name: Free Disk Space

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - id: ubuntu-latest
+          - id: ${{ vars.UBUNTU_MEDIUM || 'ubuntu-latest' }}
             name: Linux
           - id: windows-latest
             name: Windows

.github/workflows/release.yml

@@ -8,7 +8,7 @@ concurrency:
 jobs:
   build-and-stage-release:
     name: Build and Stage Release
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_MEDIUIM || 'ubuntu-latest' }}
     if: ${{ github.repository == 'spring-projects/spring-boot' }}
     steps:
       - name: Check Out Code
@@ -51,7 +51,7 @@ jobs:
     needs:
       - build-and-stage-release
       - verify
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_SMALL || 'ubuntu-latest' }}
     steps:
       - name: Check Out Code
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
@@ -68,7 +68,7 @@ jobs:
     needs:
       - build-and-stage-release
       - sync-to-maven-central
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_SMALL || 'ubuntu-latest' }}
     steps:
       - name: Set up JFrog CLI
         uses: jfrog/setup-jfrog-cli@9fe0f98bd45b19e6e931d457f4e98f8f84461fb5 # v4.4.1
@@ -81,7 +81,7 @@ jobs:
     needs:
       - build-and-stage-release
       - sync-to-maven-central
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_SMALL || 'ubuntu-latest' }}
     steps:
       - name: Check Out Code
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
@@ -97,7 +97,7 @@ jobs:
     needs:
       - build-and-stage-release
       - sync-to-maven-central
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_SMALL || 'ubuntu-latest' }}
     steps:
       - name: Check Out Code
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
@@ -115,7 +115,7 @@ jobs:
       - promote-release
       - publish-gradle-plugin
       - publish-to-sdkman
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_SMALL || 'ubuntu-latest' }}
     steps:
       - name: Check Out Code
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1

.github/workflows/run-system-tests.yml

@@ -8,7 +8,7 @@ concurrency:
 jobs:
   run-system-tests:
     name: 'Java ${{ matrix.java.version}}'
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_MEDIUM || 'ubuntu-latest' }}
     if: ${{ github.repository == 'spring-projects/spring-boot' }}
     strategy:
       matrix:

.github/workflows/verify.yml

@@ -21,7 +21,7 @@ on:
 jobs:
   verify:
     name: Verify
-    runs-on: ubuntu-latest
+    runs-on: ${{ vars.UBUNTU_SMALL || 'ubuntu-latest' }}
     steps:
       - name: Check Out Release Verification Tests
         uses: actions/checkout@v4