Use actions/checkout@v3 (#1029)

It is still used here and there in the CI

Author: OskarStark

.github/workflows/coding-standards.yml

@@ -26,7 +26,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v3"
 
       - name: Setup cache environment
         id: extcache

.github/workflows/static-analysis.yml

@@ -26,7 +26,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v3"
 
       - name: Setup cache environment
         id: extcache

.github/workflows/tests.yml

@@ -62,7 +62,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v3"
         with:
           fetch-depth: 2