chore(renovate): throttle down upgrade of linters & test packages

Once a month.

* Without throttling multiple test / linter packages are updated every
  day and this exceeds the review capacity of Forgejo contributors at
  the moment. Some of them even release more than once a day,
  apparently on every commit.

* Add @axe-core/playwright

renovate.json

@@ -144,8 +144,9 @@
     },
     {
       "description": "Automerge some packages when CI succeeds",
-      "extends": ["packages:linters", "packages:test"],
+      "extends": ["packages:linters", "packages:test", "schedule:monthly"],
       "matchPackageNames": [
+        "@axe-core/playwright",
         "@eslint-community/**",
         "@playwright/**",
         "@stoplight/spectral-cli",