title: Ignoring Django Migrations in pyproject.toml file for Black formatter
body: <p>I just got <a href="https://black.readthedocs.io/en/stable/index.html" rel="noreferrer">Black</a> and <a href="https://pre-commit.com/" rel="noreferrer">Pre-Commit</a> set up for my Django repository.</p>
  
  <p>I used the default config for Black from the tutorial I followed and it's been working great, but I am having trouble excluding my migrations files from it.</p>
  
  <p>Here is the default configuration I've been using:</p>
  
  <p><code>pyproject.toml</code></p>
  
  <pre><code>[tool.black]
  line-length = 79
  include = '\.pyi?$'
  exclude = '''
  /(
      \.git
    | \.hg
    | \.mypy_cache
    | \.tox
    | \.venv
    | _build
    | buck-out
    | build
    | dist
  )/
  '''
  </code></pre>
  
  <p>I used <a href="https://regex101.com" rel="noreferrer">Regex101.com</a> to make sure that <code>^.*\b(migrations)\b.*$</code> matched <code>apps/examples/migrations/test.py</code>.</p>
  
  <pre><code>[tool.black]
  line-length = 79
  include = '\.pyi?$'
  exclude = '''
  /(
      \.git
    | \.hg
    | \.mypy_cache
    | \.tox
    | \.venv
    | _build
    | buck-out
    | build
    | dist
    | ^.*\b(migrations)\b.*$
  )/
  '''
  </code></pre>
  
  <p>When I add that regex line to my config file, and run <code>pre-commit run --all-files</code>, it ignores the <code>.git</code> folder but still formats the migrations files. </p>