Bump actions/setup-dotnet from 1.7.2 to 1.8.1

Bumps [actions/setup-dotnet](https://github.com/actions/setup-dotnet) from 1.7.2 to 1.8.1.
- [Release notes](https://github.com/actions/setup-dotnet/releases)
- [Commits](actions/setup-dotnet@v1.7.2...v1.8.1)

---
updated-dependencies:
- dependency-name: actions/setup-dotnet
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -45,15 +45,15 @@ jobs:
         run: |
           git fetch --prune
       - name: 🔨 Use .NET Core 2.1 SDK
-        uses: actions/setup-dotnet@v1.7.2
+        uses: actions/setup-dotnet@v1.8.1
         with:
           dotnet-version: '2.1.x'
       - name: 🔨 Use .NET Core 3.1 SDK
-        uses: actions/setup-dotnet@v1.7.2
+        uses: actions/setup-dotnet@v1.8.1
         with:
           dotnet-version: '3.1.x'
       - name: 🔨 Use .NET Core 5.0 SDK
-        uses: actions/setup-dotnet@v1.7.2
+        uses: actions/setup-dotnet@v1.8.1
         with:
           dotnet-version: '5.0.x'
       - name: 🎁 dotnet tool restore