Use LfMergeBridge version from before breaking change

Later LfMergeBridge NuGet packages were accidentally compiled against a
version of Chorus with a breaking change in the localization manager,
which causes ChorusMerge failures. We'll pin LfMergeBridge to the
version just before the breaking change, just in case.

Author: rmunn

src/LfMerge.Core/LfMerge.Core.csproj

@@ -43,7 +43,7 @@ See full changelog at https://github.com/sillsdev/LfMerge/blob/develop/CHANGELOG
     <PackageReference Include="SIL.Bugsnag.Signed" Version="2.2.1" />
     <PackageReference Include="SIL.Chorus.Mercurial" Version="6.5.1.43" PrivateAssets="All" />
     <PackageReference Include="SIL.Chorus.ChorusMerge" Version="6.0.0-beta0055" GeneratePathProperty="true" />
-    <PackageReference Include="SIL.ChorusPlugin.LfMergeBridge" Version="4.2.0-beta*" />
+    <PackageReference Include="SIL.ChorusPlugin.LfMergeBridge" Version="4.2.0-beta0028" />
     <PackageReference Include="SIL.Chorus.LibChorus" Version="6.0.0-beta0055" />
     <PackageReference Include="SIL.Core.Desktop" Version="12.0.0" />
     <PackageReference Include="SIL.LCModel" Version="11.0.0-beta0077" />