Fix python#10768

It seems that if the mypy cache dir wasn't created, this code would do an exit, preventing the actual errors from being printed. So I've removed the exit.

Author: wyattscarpenter

mypy/main.py

@@ -1549,7 +1549,6 @@ def read_types_packages_to_install(cache_dir: str, after_run: bool) -> list[str]
             )
         else:
             sys.stderr.write("error: --install-types failed (no mypy cache directory)\n")
-        sys.exit(2)
     fnam = build.missing_stubs_file(cache_dir)
     if not os.path.isfile(fnam):
         # No missing stubs.