update CIs to use java21 branch

Author: xsalefter

.github/workflows/ci.yml

@@ -7,4 +7,4 @@ on:
 
 jobs:
   ci:
-    uses: killbill/gh-actions-shared/.github/workflows/ci.yml@main
+    uses: killbill/gh-actions-shared/.github/workflows/ci.yml@java21

.github/workflows/codeql-analysis.yml

@@ -7,4 +7,4 @@ on:
 
 jobs:
   analyze:
-    uses: killbill/gh-actions-shared/.github/workflows/codeql-analysis.yml@main
+    uses: killbill/gh-actions-shared/.github/workflows/codeql-analysis.yml@java21

.github/workflows/snapshot.yml

@@ -6,7 +6,7 @@ on:
 
 jobs:
   snapshot:
-    uses: killbill/gh-actions-shared/.github/workflows/snapshot.yml@main
+    uses: killbill/gh-actions-shared/.github/workflows/snapshot.yml@java21
     secrets:
       OSSRH_USER: ${{ secrets.OSSRH_USER }}
       OSSRH_PASS: ${{ secrets.OSSRH_PASS }}