Wrong verbosity level when specified in both config file and command line.

Bug Report

The verbosity level can be specified either on the command line (-v or -vv, etc.) or in the config file (verbosity = {number}). However, if specified in both places, what you get is the sum of the two levels.

To Reproduce

Place verbosity = 1 in the config file.
Call mypy -v ...

Expected Behavior

Verbosity 1, stderr shows LOG messages only.
Actual Behavior

Verbosity 2, stderr shows LOG messages and TRACE messages.

Your Environment

• Mypy version used: 0.931
• Mypy command-line flags: -v
• Mypy configuration options from mypy.ini (and other config files): verbosity = 1

How to fix the bug
This is in main.py process_options().

497    general_group.add_argument(
498        '-v', '--verbose', action='count', dest='verbosity',
499        help="More verbose messages")
923    # Parse config file first, so command line can override.
924    parse_config_file(options, set_strict_flags, config_file, stdout, stderr)
937    # Parse command line for real, using a split namespace.
938    special_opts = argparse.Namespace()
939    parser.parse_args(args, SplitNamespace(options, special_opts, 'special-opts:'))

Before line 939, save options.verbosity, then set it to 0.
After line 939, if options.verbosity is 0 (meaning -v was not present), then set it to the earlier saved value.

Note: if verbosity is specified nonzero in the config file, there is no way to override this with verbosity 0 on the command line. You could add a no-verbose command line option to accomplish this.

Start in main.py, in process_options() around the config-file parsing and second command-line parse described in the issue. Reproduce the combination of verbosity = 1 and -v, then inspect how options.verbosity is preserved and overridden. Done means command-line verbosity takes precedence rather than being added to the configured value.