Clarify "No errors found." message

[cben]

A really minor usability tweak, subjective, up to you if you like it.

In the context of webpack-dev-server, there are 2 async build processes, which may report success/failure:

• webpack bundle:
  • webpack 5.72.0 compiled with 2 errors in 5492 ms,
  • webpack 5.72.0 compiled successfully in 55345 ms are self-explaining.

There is sometimes a cyan "Type-checking in progress..." between them, but not always.

• TypeScript checking, which may arrive later:
  • when typescript fails, it starts with non-specific red "ERROR in ./src/..." but next line start with TS error code e.g. TS6133: , so clear enough.
  • when typescript succeeds, the green "No errors found." message may arrive later, and doesn't explain it's specifically what kind of errors. :point_left:

This PR tweaks the last case to say "No typescript errors found." for clarity.

[piotr-oles]

Maybe it would make more sense to just say "No typescript errors found."?

[cben]

Maybe it would make more sense to just say "No typescript errors found."?

Done, PTAL.

UPDATE: now also updated waitForNoErrors test helper. needs approval to re-run CI?