Reenable tests on PRs

This is better for third-party PRs, which otherwise don't show tests.

Author: sourcefrog

.github/workflows/tests.yml

@@ -19,15 +19,15 @@ on:
       - "src/**"
       - "testdata/**"
       - "tests/**"
-  # pull_request:
-  #   paths:
-  #     - ".cargo/*.toml"
-  #     - ".github/workflows/tests.yml"
-  #     - "Cargo.*"
-  #     - "mutants_attrs/**"
-  #     - "src/**"
-  #     - "testdata/**"
-  #     - "tests/**"
+  pull_request:
+    paths:
+      - ".cargo/*.toml"
+      - ".github/workflows/tests.yml"
+      - "Cargo.*"
+      - "mutants_attrs/**"
+      - "src/**"
+      - "testdata/**"
+      - "tests/**"
 
 # see https://matklad.github.io/2021/09/04/fast-rust-builds.html
 env: