Update actions/cache action to v6

Author: renovate[bot]

.github/workflows/main.yml

@@ -45,7 +45,7 @@ jobs:
         run: ./scripts/verify-encoding.ps1
 
       - name: NuGet cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: ${{ env.NUGET_PACKAGES }}
           key: ${{ runner.os }}.nuget.${{ hashFiles('**/*.csproj', '**/*.fsproj') }}

.github/workflows/nuget.yml

@@ -30,7 +30,7 @@ jobs:
         run: echo "version=$(./scripts/Get-Version.ps1 -RefName $env:GITHUB_REF)" >> $env:GITHUB_OUTPUT
 
       - name: NuGet cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: ${{ env.NUGET_PACKAGES }}
           key: release.nuget.${{ hashFiles('**/*.csproj', '**/*.fsproj') }}