.github/workflows: Use the latest checkout action

Fix the following warning:

Node.js 16 actions are deprecated. Please update the following actions to
use Node.js 20: actions/checkout@v3.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>

.github/workflows/checkpatch_pull.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@main
         with:
           ref: ${{github.event.pull_request.head.sha}}
           fetch-depth: 0

.github/workflows/checkpatch_push.yml

@@ -15,7 +15,7 @@ jobs:
         commit: ${{github.event.commits}}
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@main
         with:
           ref: ${{matrix.commit.id}}
           fetch-depth: 2

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
         compiler: [gcc, clang]
         arch: [x86_64]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@main
       - name: Install build-essential
         run: |
           sudo apt-get update

.github/workflows/coverity.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Project
-        uses: actions/checkout@v3
+        uses: actions/checkout@main
 
       - name: Get version
         id: get_version

.github/workflows/mail_notification.yml

@@ -17,7 +17,7 @@ jobs:
         commit: ${{github.event.commits}}
     steps:
       - name: Checkout Project
-        uses: actions/checkout@v3
+        uses: actions/checkout@main
         with:
           ref: ${{matrix.commit.id}}
           fetch-depth: 2