chore(renovate): consolidate automerge rules and update README versions

Merge the separate actions/checkout packageRule into the existing
ah-annotations rule to reduce duplication. Update README examples to use
current versions (actions/checkout@v5.0.0, ah-annotations@v0.0.1).

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

README.md

@@ -14,10 +14,10 @@ Without explicit inputs the action determines the two most recent non-RC tags fr
 
 ```yaml
 steps:
-  - uses: actions/checkout@v4
+  - uses: actions/checkout@v5.0.0
     with:
       fetch-depth: 0
-  - uses: volker.raschek/ah-annotations@v1
+  - uses: volker.raschek/ah-annotations@v0.0.1
 ```
 
 ### Explicit tags
@@ -26,10 +26,10 @@ Pass `old-tag` and `new-tag` to control the commit range:
 
 ```yaml
 steps:
-  - uses: actions/checkout@v4
+  - uses: actions/checkout@v5.0.0
     with:
       fetch-depth: 0
-  - uses: volker.raschek/ah-annotations@v1.0.0
+  - uses: volker.raschek/ah-annotations@v0.0.1
     with:
       old-tag: v1.0.0
       new-tag: v2.0.0

renovate.json

@@ -41,6 +41,7 @@
       ],
       "automerge": true,
       "matchDepNames": [
+        "actions/checkout",
         "volker.raschek/ah-annotations"
       ],
       "matchUpdateTypes": [
@@ -48,21 +49,6 @@
         "minor",
         "patch"
       ]
-    },
-    {
-      "addLabels": [
-        "renovate/automerge",
-        "renovate/documentation"
-      ],
-      "automerge": true,
-      "matchDepNames": [
-        "actions/checkout"
-      ],
-      "matchUpdateTypes": [
-        "minor",
-        "patch",
-        "pinDigest"
-      ]
     }
   ],
   "postUpgradeTasks": {