fix: JS error when use lineNumberStyle() for inline line numbers

[ktmud]

Fix a JS error when using lineNumberStyle as a function for inline line numbers.

When running the tests locally, there were also two failing tests which I was not sure know how to fix.

 FAIL  __tests__/light-async.js
  ● SyntaxHighlighter renders fortran highlighted text

    expect(received).toMatchSnapshot()

    Snapshot name: `SyntaxHighlighter renders fortran highlighted text 1`

    - Snapshot  - 658
    + Received  +  25

 FAIL  __tests__/prism-async-light.js
  ● When the code split is loaded - SyntaxHighlighter renders python highlighted text after async loading python

    expect(received).toMatchSnapshot()

    Snapshot name: `When the code split is loaded - SyntaxHighlighter renders python highlighted text after async loading python 1`

    - Snapshot  - 1162
    + Received  +   25

[simmerer]

Thanks for this PR, @ktmud! Looks good to me. Tested locally, and I don't see the test failures that you experienced in those two async tests. We sorta-recently resolved some issues there.