src/libraries/tests.proj contains incorrect condition

[janvorli]

The test run complains:
F:\git\runtime4\src\libraries\tests.proj(24,11): error MSB4092: An unexpected token "==" was found at character position 25 in condition "'$(Coverage)' == 'true' == 'true' and '$(SkipCoverageReport)' != 'true'".

[danmoseley]

@safern this was broken by #33553

[safern]

I'll take a look and put up a PR in a few mins.

Tagging @safern, @ViktorHofer as an area owner