[fix]: Bumps GitVersion.Tool

Update to the latest stable version of GitVersion.Tool that supports .NET 6.
Resolves #2791.

Co-authored-by: Nick Floyd <139819+nickfloyd@users.noreply.github.com>

Author: martincostello

build/Lifetime.cs

@@ -42,7 +42,7 @@ public override void Setup(Context context)
             new Project { Name = "Octokit.Tests.Integration", Path = "./Octokit.Tests.Integration/Octokit.Tests.Integration.csproj", IntegrationTests = true }
         };
 
-        context.GitVersionToolPath = ToolInstaller.DotNetToolInstall(context, "GitVersion.Tool", "5.6.5", "dotnet-gitversion");
+        context.GitVersionToolPath = ToolInstaller.DotNetToolInstall(context, "GitVersion.Tool", "5.12.0", "dotnet-gitversion");
         ToolInstaller.DotNetToolInstall(context, "coverlet.console", "1.7.2", "coverlet");
 
         // Calculate semantic version.