Improve error message when .* is used incorrectly

[gaborbernat]

The error message here complains about a right parenthesis missing, though that's not the issue:

    raise InvalidRequirement(str(e)) from e
packaging.requirements.InvalidRequirement: Expected closing RIGHT_PARENTHESIS
    black (>=20.*) ; extra == 'format'
          ~~~~~^

[pradyunsg]

Does the following seem more understandable?

packaging.requirements.InvalidRequirement: Expected matching RIGHT_PARENTHESIS for LEFT_PARENTHESIS, after version specifier
    black (>=20.*) ; extra == 'format'
          ~~~~~^

[pradyunsg]

packaging.requirements.InvalidRequirement: .* suffix can only be used with `==` or `!=` operators
    black (>=20.*) ; extra == 'format'
           ~~~~~^

TBH, we can also do this which is much clearer.

[pradyunsg]

[pradyunsg]

#662 does both these things

[gaborbernat]

THanks!