chore: upgrade gh actions

Author: ascott18

.github/workflows/ci.yml

@@ -16,9 +16,8 @@ jobs:
       uses: actions/setup-dotnet@v2
       with:
         dotnet-version: | 
-          6.0.x
-          7.0.x
           8.0.x
+          9.0.x
         include-prerelease: true
     - name: Build
       run: dotnet build --configuration Release

.github/workflows/release.yml

@@ -14,9 +14,8 @@ jobs:
       uses: actions/setup-dotnet@v2
       with:
         dotnet-version: | 
-          6.0.x
-          7.0.x
           8.0.x
+          9.0.x
         include-prerelease: true
     - name: Set VERSION
       run: echo "VERSION=${GITHUB_REF/refs\/tags\//}" >> $GITHUB_ENV