Fix excluding the merge commit from gitlint

This wasn't working properly, add a -x because i am still mesmerized by
the fact that it was working on my local laptop and fail in CI.

Author: chmouel

.tekton/linter.yaml

@@ -65,9 +65,10 @@ spec:
               image: jorisroovers/gitlint
               workingDir: $(workspaces.source.path)
               script: |
+                set -x
                 git config --global --add safe.directory /workspace/source
                 # don't lint merge commit
-                git log -1 |grep -q '^Merge:' && exit 0
+                git log -1 |grep -E -q '^Merge:' && exit 0
                 gitlint --commit "$(git log --format=format:%H --no-merges -1)" --ignore "Merge branch"
 
       - name: yamllint