Add xunit as a possible test runner indicator
Add xunit as a possible test runner indicator

This appears to be the cause of failures for the GetExecutablePath test.
Since we're using a new runner, it needs to be added to the pattern match
possibilities.

AndyGerlicher/msbuild,chipitsine/msbuild,AndyGerlicher/msbuild,nikson/msbuild,sean-gilliam/msbuild,mono/msbuild,yazeng/msbuild,LordJZ/msbuild,Microsoft/msbuild,ValMenn/msbuild,nikson/msbuild,ValMenn/msbuild,Microsoft/msbuild,yazeng/msbuild,cdmihai/msbuild,mono/msbuild,yazeng/msbuild,jeffkl/msbuild,rainersigwald/msbuild,ValMenn/msbuild,rainersigwald/msbuild,LordJZ/msbuild,Microsoft/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,ValMenn/msbuild,zima2219981998/msbuilding,sean-gilliam/msbuild,jeffkl/msbuild,nikson/msbuild,cdmihai/msbuild,cdmihai/msbuild,sean-gilliam/msbuild,LordJZ/msbuild,chipitsine/msbuild,sean-gilliam/msbuild,chipitsine/msbuild,mono/msbuild,danteinforno/msbuild,AndyGerlicher/msbuild,danteinforno/msbuild,jeffkl/msbuild,rainersigwald/msbuild,chipitsine/msbuild,danteinforno/msbuild,mono/msbuild,cdmihai/msbuild,nikson/msbuild,Microsoft/msbuild,zima2219981998/msbuilding,rainersigwald/msbuild,zima2219981998/msbuilding