Correctly trims values during wheel WHEEL file parsing (#7770)
## Summary
My last changes (#6616) used by mistake == instead of !=.
:disappointed_relieved: Making values currently never trimmed despite
what we wanted.
Values should now be trimmed if needed.
Also removes the trim of the header name, because if a header contains
spaces, the header will be skipped by the mailparse crate in the first
place.
## Test Plan
- A unit test has been added to validate that we correctly trim values.
- A unit test has been added to validate the header names containing
spaces are skipped.
