x/tools/gopls: CL 202581 broke tests at tip

[stamblerre]

Example logs: https://build.golang.org/log/b25de7d549ecbd0ae1ee4b93722a2584b4efe3ac

#34348 will help us catch these issues in advance in the future.

[stamblerre]

https://golang.org/cl/204041 fixed the majority of these failures.
The remaining failure has been diagnosed with a test case in go/ast (see https://golang.org/cl/204197).

[stamblerre]

This has been fixed as of https://golang.org/cl/204202.