internal/lsp: use ForTest package name when running test command

Executing the "go test" command did pass Package.PkgPath() as first
argument to the go invokation before. That failed when using test
packages with _test suffix.

The "go test" command now use Package.ForTest() instead.

Fixes golang/go#43037

Change-Id: Iea1a0e0c949a53770c1d3e1126a16a9c4952a53f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/275496
Trust: Pontus Leitzler <[email protected]>
Run-TryBot: Pontus Leitzler <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Rebecca Stambler <[email protected]>

Author: leitzler

internal/lsp/command.go

@@ -311,7 +311,7 @@ func (s *Server) runTests(ctx context.Context, snapshot source.Snapshot, uri pro
 	if len(pkgs) == 0 {
 		return fmt.Errorf("package could not be found for file: %s", uri.SpanURI().Filename())
 	}
-	pkgPath := pkgs[0].PkgPath()
+	pkgPath := pkgs[0].ForTest()
 
 	// create output
 	buf := &bytes.Buffer{}