Fix convergence CI: only run on push to master and PRs

Previously triggered on every push to every branch, running expensive
1D/2D/temporal/Sod jobs (60-90 min total) on every dev push. Now
triggers on: push to master, any pull_request, or workflow_dispatch.

Author: sbryngelson

.github/workflows/convergence.yml

@@ -2,6 +2,8 @@ name: Convergence
 
 on:
   push:
+    branches: [master]
+  pull_request:
   workflow_dispatch:
 
 env: