chore(ci): properly checkout pull request HEAD instead of merge commit in gh actions.

See https://github.com/actions/checkout#checkout-pull-request-head-commit-instead-of-merge-commit.

Signed-off-by: Federico Di Pierro <nierro92@gmail.com>

.github/workflows/ci.yml

@@ -14,6 +14,7 @@ jobs:
         uses: actions/checkout@v3
         with:
           fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Update base image
         run: sudo apt update -y
@@ -47,6 +48,7 @@ jobs:
         uses: actions/checkout@v3
         with:
           fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Update base image
         run: sudo apt update -y
@@ -80,6 +82,7 @@ jobs:
         uses: actions/checkout@v3
         with:
           fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Update base image
         run: sudo apt update -y
@@ -113,6 +116,7 @@ jobs:
         uses: actions/checkout@v3
         with:
           fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Update base image
         run: sudo apt update -y
@@ -151,6 +155,7 @@ jobs:
         with:
           fetch-depth: 0
           path: falco
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Link falco repo to /source/falco
         run: |