Add ref:main in GH workflow for pulling eqWAlizer

Summary: Apparently needed even in `checkout@v3/v4` to include all commits without delay according to actions/checkout#439.

Reviewed By: alanz

Differential Revision: D60391729

fbshipit-source-id: 4c0a8c4073f4a3c7842b9bc8aa24ed00d1a462ac

Author: VLanvin

.github/workflows/ci.yml

@@ -46,6 +46,7 @@ jobs:
         with:
           repository: WhatsApp/eqwalizer
           path: eqwalizer
+          ref: main
       - name: Set up GraalVM
         if: matrix.platform-arch != 'ubuntu-20.04-arm'
         uses: graalvm/setup-graalvm@v1