fix: disable mintmaker to run pipeline-migration-tool (#16598)

When mintmaker bumps tekton resources it is failing on running the
pipeline-migration-tool. This runs as a post upgrade task and fails when
trying to run against tekton bundles. Disabling this to allow CI checks
to pass and merge updated pipeline bundles.

Signed-off-by: Ryan Williams <3375653+ryankwilliams@users.noreply.github.com>

renovate.json

@@ -4,6 +4,9 @@
   "tekton": {
     "enabled": true,
     "automerge": true,
-    "schedule": ["* */12 * * 1-5"]
+    "schedule": ["* */12 * * 1-5"],
+    "postUpgradeTasks": {
+      "commands": []
+    }
   }
 }