Skip {types-,}protobuf upgrades in Renovate (#452)

We [previously ignored these in Dependabot][1]; should do the same in
Renovate. #451 is failing because it's attempting to bump these.

Not entirely sure on the syntax here; I'm trying to follow the
connect-python approach with otel:
https://github.com/connectrpc/connect-python/blob/f188e7d0452be8a1ad04e308754852c76ee62c4d/renovate.json#L31-L37.

[1]:
328d768#diff-dd4fbda47e51f1e35defb9275a9cd9c212ecde0b870cba89ddaaae65c5f3cd28L13-L14

Author: stefanvanburen

.github/renovate.json5

@@ -30,6 +30,15 @@
       // when necessary.
       "enabled": false
     },
+    {
+      "matchCategories": ["python"],
+      "matchPackageNames": [
+        "protobuf",
+        "types-protobuf"
+      ],
+      // We manage these dependencies ourselves.
+      "enabled": false
+    },
     {
       "matchCategories": [
         "python"