Empy v4 incompatibility

[at-wat]

Pip-installed bloom command is now broken due to a new major version of empy which bloom is not compatible with.

https://github.com/openspur/ypspur_ros/actions/runs/7470348743/job/20328896746#step:4:136

 ==> In place processing templates in 'debian' folder.
Expanding 'debian/control.em' -> 'debian/control'
Traceback (most recent call last):
  File "/usr/bin/git-bloom-generate", line 8, in <module>
    sys.exit(main())
  File "/usr/lib/python3.9/site-packages/bloom/commands/git/generate.py", line 252, in main
    run_generator(generator, args)
  File "/usr/lib/python3.9/site-packages/bloom/commands/git/generate.py", line 163, in run_generator
    try_execute('generator post_rebase', msg,
  File "/usr/lib/python3.9/site-packages/bloom/commands/git/generate.py", line 101, in try_execute
    retcode = func(*args, **kwargs)
  File "/usr/lib/python3.9/site-packages/bloom/generators/debian/generator.py", line 815, in post_rebase
    data = self.generate_debian(package, distro)
  File "/usr/lib/python3.9/site-packages/bloom/generators/debian/generator.py", line 946, in generate_debian
    template_files = process_template_files('.', subs)
  File "/usr/lib/python3.9/site-packages/bloom/generators/debian/generator.py", line 558, in process_template_files
    return __process_template_folder(debian_dir, subs)
  File "/usr/lib/python3.9/site-packages/bloom/generators/debian/generator.py", line 535, in __process_template_folder
    result = em.expand(template, **subs)
  File "/usr/bin/em.py", line 5605, in expand
    interpreter = Interpreter(**kwargs)
  File "/usr/bin/em.py", line 4103, in __init__
    raise CompatibilityError("unrecognized Interpreter constructor keyword arguments; when calling expand, use locals dictionary instead of keywords: %s" % keys, keys=keys)
em.CompatibilityError: unrecognized Interpreter constructor keyword arguments; when calling expand, use locals dictionary instead of keywords: ['BugTracker', 'BuildDepends', 'Conflicts', 'Date', 'DebianInc', 'Depends', 'Description', 'Distribution', 'Homepage', 'InstallationPrefix', 'Licenses', 'Maintainer', 'Maintainers', 'Name', 'Package', 'Replaces', 'Rosdistro', 'Source', 'Version', 'YYYY', 'changelogs', 'debhelper_version', 'format', 'release_tag']

<== Error running command '['/usr/bin/git-bloom-generate', '-y', 'rosdebian', '--prefix', 'release/noetic', 'noetic', '-i', '1', '--os-name', 'ubuntu']'

Adding version constraint to install_requires should workaround this.