chore(ci): Drop MSRV:1 patch field

This was missed when I did MSRV:3

This make it less annoying for people to keep up on every patch with
their own MSRVs.

.github/renovate.json5

@@ -45,6 +45,7 @@
       matchPackageNames: [
         'MSRV:1',
       ],
+      extractVersion: '^(?<version>\\d+\\.\\d+)',  // Drop the patch version
       schedule: [
         '* * * * *',
       ],