line highlighting: v3 matching algorithm will not match bare comments

[teamdandelion]

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Describe the bug

Consider the following python code snippet (I've substituted ' for ` for clarity)

'''python
# This comment is unimportant
# This comment is important, and should be highlighted! # [!code highlight]
'''

Or the following:

'''python{2}
# This comment is unimportant
# This comment is important, and should be highlighted!
'''

In the v3 algorithm, in both cases, it will not highlight the second line. Instead, it will append an extra # symbol at the end of the line.

Using the v1 algorithm, it correctly highlights both lines.

Reproduction

Included; see description

Contributes

• I am willing to submit a PR to fix this issue
• I am willing to submit a PR with failing tests