Revert "GHA: Test against Java 25"

This reverts commit ca69829.

Reason for revert: Temurin JDK 25 not yet available

Change-Id: I5bd479e08c97adea519a5fe121807045be10a4cf
Reviewed-on: https://review.couchbase.org/c/couchbase-jvm-clients/+/234020
Tested-by: David Nault <[email protected]>
Reviewed-by: David Nault <[email protected]>

Author: dnault

.github/workflows/integration-test.yml

@@ -23,7 +23,7 @@ jobs:
           - server: '7.6.5'
             nodes: 3
             java-distribution: 'temurin'
-            java-version: '25'
+            java-version: '21'
 
           - server: 'community-7.6.2'
             nodes: 3