chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/master_altinn-testtools-token-generator.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: windows-latest
     steps:
       - name: 'Checkout GitHub Action'
-        uses: actions/checkout@v2
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
 
       - name: Setup DotNet ${{ env.DOTNET_VERSION }} Environment
         uses: actions/setup-dotnet@v1