Bump actions/upload-artifact from 5 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/dotnet.yaml

@@ -209,12 +209,12 @@ jobs:
     - name: Pack
       run: nix develop --command dotnet pack --configuration Release
     - name: Upload NuGet artifact (lib)
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: nuget-package-lib
         path: WoofWare.NUnitTestRunner.Lib/bin/Release/WoofWare.NUnitTestRunner.Lib.*.nupkg
     - name: Upload NuGet artifact (tool)
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: nuget-package-tool
         path: WoofWare.NUnitTestRunner/bin/Release/WoofWare.NUnitTestRunner.*.nupkg

flake.lock

@@ -20,11 +20,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1764947035,
-        "narHash": "sha256-EYHSjVM4Ox4lvCXUMiKKs2vETUSL5mx+J2FfutM7T9w=",
+        "lastModified": 1765457389,
+        "narHash": "sha256-ddhDtNYvleZeYF7g7TRFSmuQuZh7HCgqstg5YBGwo5s=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "a672be65651c80d3f592a89b3945466584a22069",
+        "rev": "f997fa0f94fb1ce55bccb97f60d41412ae8fde4c",
         "type": "github"
       },
       "original": {