Github Actions: Update to actions/checkout@v3

Author: mbrossard

.github/workflows/linux.yml

@@ -30,7 +30,7 @@ jobs:
           ${{ runner.os }}-pip-
 
     - name: Checkout source files
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
       with:
         fetch-depth: 0
 

.github/workflows/pr.yml

@@ -30,7 +30,7 @@ jobs:
           ${{ runner.os }}-pip-
 
     - name: Checkout source files
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
       with:
         fetch-depth: 0
 

.github/workflows/windows.yml

@@ -24,7 +24,7 @@ jobs:
           ${{ runner.os }}-pip-
 
     - name: Checkout source files
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
       with:
         fetch-depth: 0