Switch from 7z to zip for test archive

This not only gets us able to address #125, but allows the test to run on .NET Core runtimes as well, since the 7z library we were using only ran on net461.
The test from #125 is still broken though, on account of not regularly running.

Author: AArnott

src/NerdBank.GitVersioning.Tests/NerdBank.GitVersioning.Tests.csproj

@@ -25,14 +25,13 @@
     <EmbeddedResource Include="ManagedGit\tree*" />
     <EmbeddedResource Include="test.vcprj" />
     <EmbeddedResource Include="test.prj" />
-    <EmbeddedResource Include="repos\submodules.7z" />
+    <EmbeddedResource Include="repos\*" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Nerdbank.GitVersioning.Tasks\Nerdbank.GitVersioning.Tasks.csproj" />
     <ProjectReference Include="..\NerdBank.GitVersioning\NerdBank.GitVersioning.csproj" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="7z.NET" Version="1.0.3" />
     <PackageReference Include="Newtonsoft.Json.Schema" Version="3.0.10" />
     <PackageReference Include="System.Collections.Immutable" Version="1.5.0" />
     <PackageReference Include="Microsoft.Build" Version="15.1.548" ExcludeAssets="runtime" />

src/NerdBank.GitVersioning.Tests/TestUtilities.cs

@@ -1,7 +1,4 @@
-#if NET461
-using SevenZipNET;
-#endif
-using Validation;
+using Validation;
 
 using System;
 using System.Collections.Generic;
@@ -67,36 +64,19 @@ internal static void ExtractEmbeddedResource(string resourcePath, string extract
 
     internal static ExpandedRepo ExtractRepoArchive(string repoArchiveName)
     {
-#if NET461
         string archiveFilePath = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
         string expandedFolderPath = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
 
-        ExtractEmbeddedResource($"repos.{repoArchiveName}.7z", archiveFilePath);
+        ExtractEmbeddedResource($"repos.{repoArchiveName}.zip", archiveFilePath);
         try
         {
-            for (int retryCount = 0; ; retryCount++)
-            {
-                try
-                {
-                    var extractor = new SevenZipExtractor(archiveFilePath);
-                    extractor.ExtractAll(expandedFolderPath);
-                    return new ExpandedRepo(expandedFolderPath);
-                }
-                catch (System.ComponentModel.Win32Exception) when (retryCount < 2)
-                {
-                }
-            }
+            System.IO.Compression.ZipFile.ExtractToDirectory(archiveFilePath, expandedFolderPath);
+            return new ExpandedRepo(expandedFolderPath);
         }
         finally
         {
-            if (File.Exists(archiveFilePath))
-            {
-                File.Delete(archiveFilePath);
-            }
+            File.Delete(archiveFilePath);
         }
-#else
-        throw new PlatformNotSupportedException();
-#endif
     }
 
     internal class ExpandedRepo : IDisposable