Add a CI check to enforce that files use git lfs when necessary. (#2025)

* Add a CI check to enforce that files use git lfs when necessary.

* Remove echo.

* Improve error message.

* Improve error message.

* Update scripts/enforce_git_lfs.sh

Co-authored-by: Jake Wharton <jw@squareup.com>

* Use bash substring matching.

---------

Co-authored-by: Jake Wharton <jw@squareup.com>

.github/workflows/build.yaml

@@ -24,6 +24,7 @@ jobs:
           java-version: 21
       - uses: gradle/actions/setup-gradle@v3
 
+      - run: ./scripts/enforce_git_lfs.sh
       - run: ./gradlew kotlinUpgradeYarnLock build -PredwoodNoApps
 
   emulator-tests:

scripts/enforce_git_lfs.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+
+output=$(git checkout .)
+
+if [[ output == *"files that should have been pointers, but weren't"* ]]; then
+    echo "Error: Encountered files that should have been checked in using Git LFS, but weren't."
+    exit 1
+else
+    exit 0
+fi