Disable renovating Bazel dependencies (#38)

We fixed our organization-wide renovate setup but now we're starting to
renovate Bazel deps in this ruleset. Rulesets, unlike other
repositories, should want to preserve oldest possible versions. To that
end, disable renovating Bazel files in this repo.

.github/renovate.json

diff --git a/.github/renovate.json b/.github/renovate.json
index 4039f18..b6ecf26 100644
--- a/.github/renovate.json
+++ b/.github/renovate.json
@@ -10,9 +10,9 @@
     ],
     "packageRules": [
       {
-        "matchFiles": ["MODULE.bazel"],
+        "matchFileNames": ["**/MODULE.bazel", "**/.bazelversion"],
         "enabled": false
       }
     ]
   }
-  
\ No newline at end of file
+