ci: cache mongodb image to avoid rate limiting (#11529)

Adding usage of `ScribeMD/docker-cache` to cache the mongodb image.

We utilize the
[supercharge/mongodb-github-action](https://github.com/supercharge/mongodb-github-action)
for pulling and starting our mongo image. This would at times cause `You
have reached your unauthenticated pull rate limit` errors because of how
many jobs our CI spins up at one time.

.github/workflows/main.yml

@@ -417,6 +417,7 @@ jobs:
       POSTGRES_USER: postgres
       POSTGRES_PASSWORD: postgres
       POSTGRES_DB: payloadtests
+      MONGODB_VERSION: 6.0
 
     steps:
       - uses: actions/checkout@v4
@@ -456,8 +457,14 @@ jobs:
           echo "POSTGRES_URL=postgresql://$POSTGRES_USER:$POSTGRES_PASSWORD@localhost:5432/$POSTGRES_DB" >> $GITHUB_ENV
         if: matrix.database == 'postgres'
 
+      # Avoid dockerhub rate-limiting
+      - name: Cache Docker images
+        uses: ScribeMD/docker-cache@0.5.0
+        with:
+          key: docker-${{ runner.os }}-mongo-${{ env.MONGODB_VERSION }}
+
       - name: Start MongoDB
-        uses: supercharge/mongodb-github-action@1.11.0
+        uses: supercharge/mongodb-github-action@1.12.0
         with:
           mongodb-version: 6.0
         if: matrix.database == 'mongodb'