[KEYCLOAK-17326] Fix:

$ git diff --name-only HEAD^
fatal: ambiguous argument 'HEAD^': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

GHA failure on 'Test Clustering on Wildfly' phase. See e.g. recent:
  https://github.com/keycloak/keycloak/pull/7705/checks?check_run_id=2023996258

Signed-off-by: Jan Lieskovsky <jlieskov@redhat.com>

.github/workflows/ci.yml

@@ -187,6 +187,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
+        with:
+          fetch-depth: 2
 
       - name: Check whether this phase should run
         run: echo "GIT_DIFF=$[ $( git diff --name-only HEAD^ | egrep -ic 'crossdc|infinispan' ) + $( git diff HEAD^ pom.xml | egrep -ic '\+\s+<wildfly.version>' ) ]" >> $GITHUB_ENV