Bump Polyfill and System.Text.Json (#308)

Bumps Polyfill from 8.6.0 to 8.6.1
Bumps System.Text.Json from 9.0.6 to 9.0.7

---
updated-dependencies:
- dependency-name: Polyfill
  dependency-version: 8.6.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: System.Text.Json
  dependency-version: 9.0.7
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]

src/Directory.Packages.props

@@ -6,9 +6,9 @@
   <ItemGroup>
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.0-beta.2" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
-    <PackageVersion Include="Polyfill" Version="8.6.0" />
+    <PackageVersion Include="Polyfill" Version="8.6.1" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.156" />
-    <PackageVersion Include="System.Text.Json" Version="9.0.6" />
+    <PackageVersion Include="System.Text.Json" Version="9.0.7" />
     <PackageVersion Include="Verify" Version="30.4.0" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />
     <PackageVersion Include="NUnit" Version="4.3.2" />