Bump VSThreadingVersion from 17.7.30 to 17.8.14 (#715)

Bumps `VSThreadingVersion` from 17.7.30 to 17.8.14.

Updates `Microsoft.VisualStudio.Threading` from 17.7.30 to 17.8.14
- [Release notes](https://github.com/microsoft/vs-threading/releases)
- [Commits](https://github.com/microsoft/vs-threading/commits)

Updates `Microsoft.VisualStudio.Threading.Analyzers` from 17.7.30 to 17.8.14
- [Release notes](https://github.com/microsoft/vs-threading/releases)
- [Commits](https://github.com/microsoft/vs-threading/commits)

Updates `Microsoft.VisualStudio.Validation` from 17.6.11 to 17.8.8
- [Release notes](https://github.com/microsoft/vs-validation/releases)
- [Commits](https://github.com/microsoft/vs-validation/commits)

---
updated-dependencies:
- dependency-name: Microsoft.VisualStudio.Threading
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: Microsoft.VisualStudio.Threading.Analyzers
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: Microsoft.VisualStudio.Validation
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Directory.Packages.props

@@ -6,7 +6,7 @@
     <CentralPackageTransitivePinningEnabled>true</CentralPackageTransitivePinningEnabled>
     <BenchmarkDotNetVersion>0.13.12</BenchmarkDotNetVersion>
     <AspNetCoreVersion>2.2.0</AspNetCoreVersion>
-    <VSThreadingVersion>17.7.30</VSThreadingVersion>
+    <VSThreadingVersion>17.8.14</VSThreadingVersion>
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="BenchmarkDotNet.Diagnostics.Windows" Version="$(BenchmarkDotNetVersion)" />