devel/ghpr: update to v3

[ngie]

Summary

v3 makes the following high-level changes apart from the standard
version update described in [1]:

• pyproject.toml / PEP-517 using setuptools_scm integration.
• Now the package is prefixed with PYTHON_PKGNAMEPREFIX so multiple versions of the package can be built with different versions of python and installed concurrently (if one decided to do that).
• LICENSE.md from the latest version is used/incorporated into the end-resulting package.

1. https://github.com/bsdimp/ghpr/releases/tag/v3

Test Plan

The new version installs cleanly on my machine:

% ghpr --help
usage: ghpr [-h] [--staging-branch STAGING_BRANCH] [-v] [-n] {init,stage,push,unstage,status} ...

GitHub Pull Request landing tool for FreeBSD

positional arguments:
  {init,stage,push,unstage,status}
                        Command to run
    init                Initialize staging branch
    stage               Stage a PR for landing
    push                Push staged PRs to FreeBSD
    unstage             Remove a staged PR
    status              Show staging branch status

options:
  -h, --help            show this help message and exit
  --staging-branch STAGING_BRANCH
                        Name of staging branch (default: staging)
  -v, --verbose         Print all commands before executing them
  -n, --dry-run         Show what would be done without actually doing it (automatically prints commands)

Examples:
  # Initialize staging branch
  ghpr init

  # Stage a PR for landing
  ghpr stage 1234

  # If rebase has conflicts, resolve them and continue
  git add <resolved-files>
  ghpr stage --continue 1234

  # Stage multiple PRs
  ghpr stage 1234
  ghpr stage 1235

  # Check status
  ghpr status

  # Remove a PR if you change your mind
  ghpr unstage 1234

  # Push all staged PRs to FreeBSD
  ghpr push
        
% which ghpr
/usr/local/bin/ghpr
% pkg info | grep ghpr
py311-ghpr-3                   GitHub Pull Request landing tool for FreeBSD

[ngie]

Bump the minimum python3 version to 3.10

Although it's not strictly required with the idioms in use, it makes
support for the package. Moreover, I added a 3.10 constraint when I
introduced the pyproject.toml change upstream, so make the ports
Makefile consistent with the pyproject.toml file.

[ngie]

Resolve complaints from portlint

[imp]

Thanks. Didn't puzzle out last night the setuptool dependency.