update branch matching in CI

Author: jsdw

.github/workflows/rust.yml

@@ -9,13 +9,13 @@ on:
       # If we want to backport changes to an old release, push a branch
       # eg v0.40.x and CI will run on it. PRs merging to such branches 
       # will also trigger CI.
-      - v0.*.x
+      - v0.[0-9]+.x
   pull_request:
     # Run jobs for any external PR that wants
     # to merge to master, too:
     branches:
       - master
-      - v0.*.x
+      - v0.[0-9]+.x
 
 concurrency:
   group: ${{ github.ref }}-${{ github.workflow }}