ci: run the focused mixer gates on the proof update

Author: richiemcilroy

.github/workflows/fix-instant-mixer-proof.yml

@@ -1,5 +1,8 @@
 name: Instant mixer alignment proof
 on:
+  push:
+    branches: [ci/fixproof-instant-mixer]
+    paths: [.github/workflows/fix-instant-mixer-proof.yml]
   workflow_dispatch:
     inputs:
       fixtures:
@@ -60,10 +63,10 @@ jobs:
       - name: Stop while paused
         run: cargo test -p cap-recording --lib --profile ci-verify --locked mixed_pipeline_stop_ -- --nocapture
       - name: Build fixture probe
-        if: inputs.fixtures != false
+        if: github.event_name == 'workflow_dispatch' && inputs.fixtures != false
         run: scripts/verify/run.sh fast --suites export --no-run
       - name: Twenty fresh generations
-        if: inputs.fixtures != false
+        if: github.event_name == 'workflow_dispatch' && inputs.fixtures != false
         env:
           CAP_VERIFY_TIER: fast
           CAP_VERIFY_LOG: cap_recording::output_pipeline=debug