Bump AltCover from 8.6.125 to 8.7.3 (jstedfast#1730)

Bumps [AltCover](https://github.com/SteveGilham/altcover) from 8.6.125 to 8.7.3.
- [Release notes](https://github.com/SteveGilham/altcover/releases)
- [Changelog](https://github.com/SteveGilham/altcover/blob/master/ReleaseNotes%20-%20Previously.md)
- [Commits](https://github.com/SteveGilham/altcover/commits)

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

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UnitTests/UnitTests.csproj

@@ -23,7 +23,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="AltCover" Version="8.6.125" />
+    <PackageReference Include="AltCover" Version="8.7.3" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageReference Include="nunit" Version="4.1.0" />