Patch attached

From the Getopt::Long changes:
```
Changes in version 2.55
-----------------------
* Fix long standing bug that duplicate options were not detected when
  the options differ in case while ignore_case is in effect.
  This will now yield a warning and become a fatal error in a future
  release.
```

Current version is 2.57


```
git-2.43.0 🐧 perl -Iperl git-send-email.perl --help
Duplicate specification "cc-cover|cc-cover!" for option "cc-cover"
Duplicate specification "no-cc-cover" for option "no-cc-cover"
Duplicate specification "to-cover|to-cover!" for option "to-cover"
Duplicate specification "no-annotate" for option "no-annotate"
Duplicate specification "no-format-patch" for option "no-format-patch"
Duplicate specification "no-signed-off-cc|no-signed-off-by-cc" for option "no-signed-off-cc"
Duplicate specification "no-signed-off-cc|no-signed-off-by-cc" for option "no-signed-off-by-cc"
Duplicate specification "no-validate" for option "no-validate"
Duplicate specification "no-chain-reply-to" for option "no-chain-reply-to"
```

`"option!" => \$value`

*automatically* supports both `--option` and `--no-option` and `--nooption`

See the docs for Getopt::Long:
```
 The argument specification can be

 !   The option does not take an argument and may be negated by
     prefixing it with "no" or "no-". E.g. "foo!" will allow "--foo" (a
     value of 1 will be assigned) as well as "--nofoo" and "--no-foo" (a
     value of 0 will be assigned). If the option has aliases, this
     applies to the aliases as well.

     Using negation on a single letter option when bundling is in effect
     is pointless and will result in a warning.
```


-- 
H.Merijn Brand  https://tux.nl   Perl Monger   http://amsterdam.pm.org/
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