fix(renovate): escape slash in matchStrings and add automerge rule for actions/checkout

Escape the forward slash in the ah-annotations regex pattern to ensure
correct matching. Add a packageRule to automerge minor, patch, and
pinDigest updates for actions/checkout.

Co-authored-by: Copilot <copilot@github.com>

renovate.json

@@ -13,7 +13,7 @@
         "^README\\.md$"
       ],
       "matchStrings": [
-        "uses: volker\\.raschek/ah-annotations@(?<currentValue>[^\\s\"']+)"
+        "uses: volker\\.raschek\/ah-annotations@(?<currentValue>[^\\s\"']+)"
       ],
       "depNameTemplate": "volker.raschek/ah-annotations",
       "packageNameTemplate": "https://git.cryptic.systems/volker.raschek/ah-annotations",
@@ -48,6 +48,21 @@
         "minor",
         "patch"
       ]
+    },
+    {
+      "addLabels": [
+        "renovate/automerge",
+        "renovate/documentation"
+      ],
+      "automerge": true,
+      "matchDepNames": [
+        "actions/checkout"
+      ],
+      "matchUpdateTypes": [
+        "minor",
+        "patch",
+        "pinDigest"
+      ]
     }
   ],
   "postUpgradeTasks": {