Leave the Gradle plugin's tests out of the JDK 27 job

On JDK 27 every TestKit build failed with "BUG! exception in phase 'semantic
analysis' in source unit '_BuildScript_' Unsupported class file major
version 71": Gradle 9.7.1 does not run on Java 27, and TestKit runs the
builds on the test JVM. The formatter's own tests all pass there.

Each leg of the matrix now names its extra Gradle arguments and the reason
for them, empty for 25 and 26. The 27 leg passes -x
:gradle-open-java-format:test, and the job shows the reason as a notice,
so it is visible in the run and not only in a YAML comment.

Author: abashev

.github/workflows/ci.yml

@@ -48,7 +48,19 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        jdk: [25, 26, 27]
+        include:
+          - jdk: 25
+            gradle_args: ''
+            gradle_args_reason: ''
+          - jdk: 26
+            gradle_args: ''
+            gradle_args_reason: ''
+          - jdk: 27
+            gradle_args: -x :gradle-open-java-format:test
+            gradle_args_reason: >-
+              Gradle 9.7.1 does not run on Java 27 yet, and the Gradle plugin's tests run their TestKit builds on
+              the test JVM, where they fail with "Unsupported class file major version 71". Those tests are left
+              out until the wrapper's Gradle supports Java 27.
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
@@ -66,10 +78,17 @@ jobs:
           distribution: temurin
           java-version: '21'
 
+      - name: Explain the extra Gradle arguments
+        if: ${{ matrix.gradle_args != '' }}
+        env:
+          GRADLE_ARGS: ${{ matrix.gradle_args }}
+          REASON: ${{ matrix.gradle_args_reason }}
+        run: echo "::notice title=JDK ${{ matrix.jdk }} runs with $GRADLE_ARGS::$REASON"
+
       # Gradle does not look into the runner's tool cache, so it is told where the test JDK is.
       - name: Build
         run: >-
-          ./gradlew test -PjavaRuntime=${{ matrix.jdk }}
+          ./gradlew test -PjavaRuntime=${{ matrix.jdk }} ${{ matrix.gradle_args }}
           -Porg.gradle.java.installations.paths=${{ steps.test-jdk.outputs.path }}
 
       - name: Publish Test Report