Bump Polyfill from 7.3.0 to 7.4.0 in /src

Bumps [Polyfill](https://github.com/SimonCropp/Polyfill) from 7.3.0 to 7.4.0.
- [Commits](SimonCropp/Polyfill@7.3.0...7.4.0)

---
updated-dependencies:
- dependency-name: Polyfill
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

src/Directory.Packages.props

@@ -13,7 +13,7 @@
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
     <PackageVersion Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.2.13" />
     <PackageVersion Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" />
-    <PackageVersion Include="Polyfill" Version="7.3.0" />
+    <PackageVersion Include="Polyfill" Version="7.4.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.141" />
     <PackageVersion Include="PropertyChanged.Fody" Version="4.1.0" />
     <PackageVersion Include="System.Runtime.InteropServices.RuntimeInformation" Version="4.3.0" />