[GitHub -> Actions] Update to .NET 9 and update actions.

.github/workflows/unit-tests.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-latest, windows-latest ]
-        dotnet-version: [ '8.0.x' ]
+        dotnet-version: [ '9.0.x' ]
 
     permissions:
       packages: write
@@ -30,15 +30,15 @@ jobs:
 
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v4.1.5
+        uses: actions/checkout@v4.2.2
 
       - name: Setup .NET ${{ matrix.dotnet-version }}
-        uses: actions/setup-dotnet@v4.0.0
+        uses: actions/setup-dotnet@v4.1.0
         with:
           dotnet-version: ${{ matrix.dotnet-version }}
 
       - name: Check Dependency Cache
-        uses: actions/cache@v4.0.2
+        uses: actions/cache@v4.1.2
         with:
           path: ${{ github.workspace }}/.nuget/packages
           key: ${{ runner.os }}-nuget-${{ hashFiles('**/*.csproj') }}