cirrus: move renovate check into validate

The renovate config is used for the renovate bot, validating this in the
prior fedora prebuild setp is just confusing and hidden.

The problem is this image is very big so it is slow to download/extract.
To speed things up given it is only a single file we check the diff if
we even changed it.

Now one could argue this should be part of the validate Makefile target
but I given the size I do not want this run by default and I am not sure
if we should do the diff check in the Makefile.

Lastly remove -it, these is meant for interactive use and throws a
warning here because we have no actual tty attached.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

contrib/cirrus/prebuild.sh

@@ -65,12 +65,6 @@ if [[ "${DISTRO_NV}" == "$PRIOR_FEDORA_NAME" ]]; then
     # Tests for pr-should-link-jira
     showrun ${SCRIPT_BASE}/pr-should-link-jira.t
 
-    msg "Checking renovate config."
-    showrun podman run -it \
-            -v ./.github/renovate.json5:/usr/src/app/renovate.json5:z \
-            ghcr.io/renovatebot/renovate:latest \
-            renovate-config-validator
-
     # Run this during daily cron job to prevent a GraphQL API change/breakage
     # from impacting every PR.  Down-side being if it does fail, a maintainer
     # will need to do some archaeology to find it.

contrib/cirrus/runner.sh

@@ -22,6 +22,10 @@ source $(dirname $0)/lib.sh
 showrun echo "starting"
 
 function _run_validate-source() {
+    # This target is only meant to be run on PRs.
+    # We need the following env vars set for the git diff check below.
+    req_env_vars CIRRUS_CHANGE_IN_REPO PR_BASE_SHA
+
     showrun make validate-source
 
     # make sure PRs have tests
@@ -29,6 +33,22 @@ function _run_validate-source() {
 
     # make sure PRs have jira links (if needed for branch)
     showrun make test-jira-links-included
+
+    # shellcheck disable=SC2154
+    head=$CIRRUS_CHANGE_IN_REPO
+    # shellcheck disable=SC2154
+    base=$PR_BASE_SHA
+    echo "_run_validate-source: head=$head  base=$base"
+    diffs=$(git diff --name-only $base $head)
+
+    # If PR touches renovate config validate it, as the image is very big only do so when needed
+    if grep -E -q "^.github/renovate.json5" <<<"$diffs"; then
+        msg "Checking renovate config."
+        showrun podman run \
+            -v ./.github/renovate.json5:/usr/src/app/renovate.json5:z \
+            ghcr.io/renovatebot/renovate:latest \
+            renovate-config-validator
+    fi
 }
 
 function _run_unit() {