Always test private modules with latest PHP version

private-modules-overrides.yml

@@ -2,6 +2,10 @@ variables:
   OPT_IN_TEST_NEXT_MINOR: 1
   OPT_IN_TEST_NEXT_MAJOR: 0
   RUN_JOB_UPGRADE_STATUS: 0
+  # Always test modules with latest PHP version.
+  PHP_VERSION: '8.3'
+  CORE_PHP_MAX: '8.3'
+  _TARGET_PHP: '8.3'
 
 .provide-info-yml-if-needed: &provide-info-yml-if-needed
   - |