build(ci): Always run "check migration" workflow (#27818)

Previously this workflow only ran when certain files were modified. This meant that we could not use GH to mark the job as "required" because the check would be missing. Changed this to always run, but skip job if relevant files were not changed.

Closes #27044

.github/file-filters.yml

@@ -71,3 +71,11 @@ migrations_added:
 
 migrations_modified:
   - modified: 'src/sentry/migrations/*'
+
+# These files will trigger our wokrflow to check if lockfile
+# updates are needed
+migration_lockfile:
+  - *backend_dependencies
+  - *backend_lintable
+  - .github/workflows/check-if-migration-is-required.yml
+  - .github/workflows/scripts/migration-check.sh

.github/workflows/check-if-migration-is-required.yml

@@ -1,20 +1,35 @@
 name: check migration
-on:
-  pull_request:
-    paths:
-      # Matches all python files regardless of directory depth.
-      - '**.py'
-      - requirements*.txt
-      - .github/workflows/check-if-migration-is-required.yml
-      - .github/workflows/scripts/migration-check.sh
+on: pull_request
 
 jobs:
+  should-check:
+    name: did files change
+    runs-on: ubuntu-20.04
+    timeout-minutes: 3
+    # Map a step output to a job output
+    outputs:
+      changed: ${{ steps.changes.outputs.migration_lockfile }}
+    steps:
+      - name: Checkout sentry
+        uses: actions/checkout@v2
+
+      - name: check if files have changed
+        uses: getsentry/paths-filter@v2
+        id: changes
+        with:
+          token: ${{ github.token }}
+          filters: .github/file-filters.yml
+
+
   main:
     name: check migration
     runs-on: ubuntu-20.04
+    needs: [should-check]
+    if: needs.should-check.outputs.changed == 'true'
 
     steps:
-      - uses: actions/checkout@v2
+      - name: Checkout sentry
+        uses: actions/checkout@v2
 
       - name: Set python version output
         id: python-version