Remove dependency diff comment if no changes in Gradle files is detected

[wzieba]

Reproduction:

1. Prepare a PR with a change to .gradle, .gradle.kts or .toml file
2. Wait for dependency diff comment to appear
3. Revert change from point 1

Expected behavior:
Dependency diff commit is removed

Actual behavior:
Dependency diff commit is not removed.

Reason: because no change is detected, the script exits early if no Gradle changes are detected. The script should remove the comment in such case:

a8c-ci-toolkit-buildkite-plugin/bin/comment_with_dependency_diff

Lines 69 to 74 in e05b61b

	if (git diff --name-status "origin/$BASE_BRANCH" | grep -E "\.gradle(\.kts)?|\.toml" --quiet); then
	echo "Gradle files have been changed. Looking for caused dependency changes"
	else
	echo "Gradle files haven't been changed. There is no need to run the diff"
	exit 0
	fi