Clean up tests workflow

Rename run_tests.yml to tests.yml, restrict push trigger to main, and
drop the unused CACHE_TARGET env var.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: skearnes

.github/workflows/run_tests.yml .github/workflows/tests.yml.github/workflows/run_tests.yml renamed to .github/workflows/tests.yml

@@ -12,14 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-name: CI
-
-on: [ pull_request, push ]
-
-env:
-  # See https://dev.to/dtinth/caching-docker-builds-in-github-actions-which-approach-is-the-fastest-a-research-18ei.
-  CACHE_TARGET: "docker.pkg.github.com/open-reaction-database/ord-interface/interface-cache"
+name: Tests
 
+on:
+  pull_request:
+  push:
+    branches:
+      - main
 
 jobs:
   test_ord_interface: