Bump Microsoft.Graph from 5.55.0 to 6.8.0

---
updated-dependencies:
- dependency-name: Microsoft.Graph
  dependency-version: 6.8.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

src/GitHubConnector.csproj

@@ -30,7 +30,7 @@
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="8.0.1" />
     <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" Version="8.0.1" />
     <PackageReference Include="Microsoft.Extensions.Logging.Console" Version="9.0.0" />
-    <PackageReference Include="Microsoft.Graph" Version="5.55.0" />
+    <PackageReference Include="Microsoft.Graph" Version="6.8.0" />
     <PackageReference Include="Octokit" Version="14.0.0" />
     <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>