Misc: allow unknown args when finding prefix #1617

Job	Run time
linux-newLTS-github--dotnet-and-xbuild	8m 41s
linux-newLTS-vanilla--newmono	6m 39s
linux-newLTS-github--dotnet-and-msbuild	7m 56s
linux-newLTS-vanilla--stockmono	5m 50s
linux-newLTS-vanilla--dotnet6	9m 38s
linux-oldLTS-github--dotnet-and-msbuild	8m 28s
linux-oldLTS-github--dotnet-and-xbuild	7m 50s
linux-oldLTS-vanilla--newmono	7m 56s
linux-oldLTS-vanilla--stockmono	5m 45s
macOS--dotnet6-and-mono	8m 19s
macOS--mono	4m 58s
windows--dotnet6	10m 42s
windows--legacyFramework	21m 23s
sanity-check	1m 12s
publish	1m 13s
	1h 56m 30s

Provide feedback