Restrict convergence CI to workflow_dispatch only

Tests are too slow (~30-45 min each job) to run on every PR push.
Manual trigger via workflow_dispatch lets you run them deliberately
when verifying numerics, not on every commit.

Author: sbryngelson

.github/workflows/convergence.yml

@@ -1,16 +1,8 @@
 name: Convergence
 
 on:
-  push:
-    branches: [master]
-  pull_request:
-    types: [opened, synchronize, reopened, ready_for_review]
   workflow_dispatch:
 
-concurrency:
-  group: ${{ github.workflow }}-${{ github.event_name == 'push' && github.sha || github.ref }}
-  cancel-in-progress: ${{ github.event_name != 'push' }}
-
 jobs:
   convergence-1d:
     name: "1D Advection Convergence"