Don't run unsupported tests on 8.6 and 9.0

https://coreos.slack.com/archives/C0235DZB0DT/p1650536467098679?thread_ts=1650512166.141439&cid=C0235DZB0DT

test/cases/gcp.sh

@@ -7,10 +7,21 @@
 # that the package from blueprint was installed.
 #
 
-set -euo pipefail
-
 source /usr/libexec/osbuild-composer-test/set-env-variables.sh
 
+if [ "${NIGHTLY:=false}" == "true" ]; then
+    case "${ID}-${VERSION_ID}" in
+        "rhel-8.6" | "rhel-9.0" )
+            echo "$0 is not enabled for ${ID}-${VERSION_ID} skipping..."
+            exit 0
+            ;;
+        *)
+            ;;
+    esac
+fi
+
+set -euo pipefail
+
 # Colorful output.
 function greenprint {
     echo -e "\033[1;32m[$(date -Isecond)] ${1}\033[0m"