CI: trim build matrix on macOS/Windows and add workflow concurrency

.github/workflows/build.yml

@@ -4,13 +4,28 @@ on:
   push:
     branches: [ 'sustaining/1.8.x','master', 'issues/**', 'features/**' ]
   pull_request:
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 jobs:
   build-maven:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
+        os: [ 'ubuntu-latest' ]
         java: [ '11', '17', '21', '25', '26' ]
-        os: [ 'ubuntu-latest', 'macos-latest', 'windows-latest' ]
+        # macOS and Windows runners are the slowest and scarcest in CI, so only
+        # smoke-test the minimum (11) and maximum (26) supported JDKs on them.
+        # Ubuntu keeps the full JDK matrix above.
+        include:
+          - os: 'macos-latest'
+            java: '11'
+          - os: 'macos-latest'
+            java: '26'
+          - os: 'windows-latest'
+            java: '11'
+          - os: 'windows-latest'
+            java: '26'
       fail-fast: false
     steps:
       - uses: actions/checkout@v6

.github/workflows/deploy.yml

@@ -6,6 +6,9 @@ on:
     branches: [ 'sustaining/1.8.x','master' ]
     workflows: ["Build","Release"]
     types: [completed]
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.workflow_run.head_branch }}
+  cancel-in-progress: false
 
 jobs:
   deploy-maven:

.github/workflows/release.yml

@@ -11,6 +11,9 @@ on:
         description: "Default version to use for new local working copy."
         required: true
         default: "X.Y.Z-SNAPSHOT"
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: false
 jobs:
   release-maven:
     runs-on: 'ubuntu-latest'