chore: Enable assembly signing for debug build

[filzrev]

This PR enable assembly signing for Debug build also.

Background
When using BenchmarkDotNet.TestAdapter and project contains net462 target.
net462 benchmarks are not shown on TestExplorer with Debug configuration.
And following error log is recorded on VS output window's Tests pane.

System.IO.FileLoadException: A strongly-named assembly is required. (Exception from HRESULT: 0x80131044)'

Currently BenchmarkDotNet sign assembly on Release build only.
This PR change this behavior to sign Debug build assembly also.

What's Tested

• BenchmarkDotNet.Samples (net462) benchmarks are shown on TestExplorer
• It can display benchmarks on TestExplorer when benchmark project don't use assembly-signing.

[AndreyAkinshin]

The current behavior of non-signed Debug builds was introduced in commit 5876f57 on April 12, 2016, by @adamsitnik. I am open to reconsidering this, but I would like to understand the use case better. Why do you want to use the Debug build of BenchmarkDotNet through VS TestExplorer?

P.S. BenchmarkDotNet intentionally creates inconveniences to prevent users from running benchmarks with non-optimized assemblies. Therefore, the absence of discovered tests with the Debug version of BenchmarkDotNet seems to be the desired behavior. 🙂

[adamsitnik]

In general the problem you have described is specific to our own solution, as all our customers use the Release builds we ship to nuget.org. But I don't mind improving our dev loop experience of course. Thanks for providing the fix @filzrev!