Add JDK25 generating Java21 bytecode (#5290)

Signed-off-by: Holger Friedrich <mail@holger-friedrich.de>

.github/workflows/ci-build.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        java: [ '21' ]
+        java: [ '21', '25' ]
         os: [ 'ubuntu-24.04' ]
     name: Build (Java ${{ matrix.java }}, ${{ matrix.os }})
     runs-on: ${{ matrix.os }}
@@ -176,7 +176,7 @@ jobs:
           mode: inline
 
       - name: Remove Label
-        if: ${{ always() && github.event.label.name == 'rebuild' }}
+        if: ${{ matrix.java == '21' && always() && github.event.label.name == 'rebuild' }}
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           PR: ${{ github.event.number }}

pom.xml

@@ -656,8 +656,17 @@ Import-Package: \
                 <requireMavenVersion>
                   <version>3.9.6</version>
                 </requireMavenVersion>
+                <requireJavaVersion>
+                  <version>[21.0,22.0),[25.0,26.0)</version>
+                </requireJavaVersion>
                 <requireJavaVersion>
                   <version>[21.0,22.0)</version>
+                  <message>++ WARNING ++ WARNING ++ WARNING ++ WARNING ++ WARNING ++ WARNING ++
+JDK 25 compiler is in use, generating Java 21 bytecode.
+This is not officially supported.
+Consider using JDK 21 for building and testing.
+++ WARNING ++ WARNING ++ WARNING ++ WARNING ++ WARNING ++ WARNING ++</message>
+                  <level>WARN</level>
                 </requireJavaVersion>
               </rules>
             </configuration>