Bump actions/cache from 3 to 4

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v3...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/_build-test.yml

@@ -71,7 +71,7 @@ jobs:
 
       # https://github.com/actions/cache/blob/main/examples.md#c---nuget
       - name: Get any cached NuGet packages from the last run
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: '~/.nuget/packages'
           key: nugetpackages-${{ runner.os }}-${{ hashFiles('source/**/*.csproj') }}