Only run GitHub Actions for tags that look like semver versions (#1484)

We had previously been running for sass_api tags, which inevitably
failed when they didn't match the pubspec version.

Author: nex3

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ env:
 on:
   push:
     branches: [main, feature.*]
-    tags: ['**']
+    tags: ['[0-9]+.[0-9]+.*']
   pull_request:
 
 jobs: