This PR aligns the type annotation of pstats.FunctionProfile.ncalls with its runtime str type.

The fact that the runtime type of pstats.FunctionProfile.ncalls is str can be verified by (1) inspecting the source code for pstats and (2) running a small test snippet:

1. in the source code for pstats, the only place where ncalls is defined seems to be

   cpython/Lib/pstats.py

   Line 372 in 6281aff

   ncalls = str(nc) if nc == cc else (str(nc) + '/' + str(cc))

   where the assigned value is always a string;

2. you can also check that stats.FunctionProfile.ncalls is a string by running the following script:

   from cProfile import Profile
   from pstats import Stats
   
   # execute random code to generate profile stats
   with Profile() as profile:
       print("foo")
   
   # get a sample function profile
   stats_profile = Stats(profile).get_stats_profile()
   function_profile = next(iter(stats_profile.func_profiles.values()))
   
   # check that the type of `function_profile.ncalls` is indeed `str`
   assert type(function_profile.ncalls) is str

I also have an open PR in typeshed to fix this issue there: python/typeshed#8712.

This change seems small and straightforward enough not to require an issue, but I am happy to open one if you think it is necessary. I also did not include any tests since this is a type annotation fix without any changes to the runtime behavior.