chore: Use git sha as checkout ref (#14)

## Which problem is this PR solving?

Updates checkout action for main and release workflows to use git sha as
ref.

.github/workflows/main.yaml

@@ -12,6 +12,8 @@ jobs:
       packages: write
     steps:
       - uses: actions/checkout@v3.5.3
+        with:
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
 
       - name: Log in to the Container registry
         uses: docker/login-action@v2.2.0

.github/workflows/pr.yaml

@@ -8,7 +8,9 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout Repo
-        uses: actions/checkout@v1
+        uses: actions/checkout@v3.5.3
+        with:
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
 
       - name: build
         run: make docker-build

.github/workflows/release.yaml

@@ -12,6 +12,8 @@ jobs:
       packages: write
     steps:
       - uses: actions/checkout@v3.5.3
+        with:
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
 
       - name: Log in to the Container registry
         uses: docker/login-action@v2.2.0