Fix test failing on Windows

[mattjohnsonpint]

For some unknown reason, my local Windows machine was giving project paths with c:\ instead of C:\, which was causing FileNameShouldBeRelative to fail. I'm still hunting down why, but this will prevent it.

Related to #1739

#skip-changelog

[mattjohnsonpint]

The test only failed on net6.0, so I thought it might be because I had 6.0.302 locally, while CI is still on 6.0.301.

So I uninstalled 6.0.302 and installed 6.0.301 (since they no longer let you install them both side-by-side). The test passed.

But then I re-installed 6.0.302, and I expected the test to fail, but it still passed - even with a full git clean and rebuild.

So either I had a bad install, or it reset something else? Not sure. Anyway, I still think we should merge this.

[SimonCropp]

IMO it would be easier to do a case insensitive startswith later in the processing

[mattjohnsonpint]

It's used here (on line 190)

sentry-dotnet/src/Sentry/Extensibility/SentryStackTraceFactory.cs

Lines 181 to 194 in f3c7949

	AttributeReader.TryGetProjectDirectory(method.Module.Assembly, out projectPath);
	}
	frame.ConfigureAppFrame(_options);
	var frameFileName = stackFrame.GetFileName();
	if (projectPath != null && frameFileName != null)
	{
	frameFileName = frameFileName.Replace(projectPath, "");
	}
	frame.FileName = frameFileName;

Unfortunately, string.Replace doesn't have an overload with comparer parameter in netstandard2.0 or net461. We would need a shim.

[mattjohnsonpint]

Either way is fine with me, if you want to take another go at it, @SimonCropp ?

[mattjohnsonpint]

Close in favor of #1791