Revert "CI: keep testing on JDK 11."

This reverts commit d752f9b.

Author: greenrobot-team

.gitlab-ci.yml

@@ -99,12 +99,13 @@ test-jdk-8:
   variables:
     TEST_JDK: 8
 
-# JDK 11 is the next oldest LTS release.
-test-jdk-11:
-  extends: .test-asan-template
-  needs: ["test-jdk-8"]
-  variables:
-    TEST_JDK: 11
+# JDK 17 is currently the default of the build image. JDK 21 LTS will arrive around September 2023.
+# JDK 17 is the latest LTS release.
+#test-jdk-17:
+#  extends: .test-asan-template
+#  needs: ["test-jdk-8"]
+#  variables:
+#    TEST_JDK: 17
 
 test-jdk-x86:
   extends: .test-template