Require Java 25, not 26

Nothing in the desktop client needs more than the FFM API, final since
Java 22. It builds, passes its tests and runs on OpenJDK 25, the current
LTS, which reaches more distributions. CI now tests on that minimum.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/test.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: 26
+          java-version: 25
           cache: maven
       # Builds ts3j from the submodule along with the client; no test needs a display or libopus.
       - run: mvn -B -f ts3-client/pom.xml verify