Unchanged lines detected as changes with difflib.HtmlDiff

Bug report

Bug description:

When running HtmlDiff on test_api_result.response.txt test_api_result.expected.txt (reported at https://github.com/jeffkaufman/icdiff/issues/223) unchanged lines are being detected as changes. Here's the setup:

import difflib
a = open("test_api_result.response.txt").readlines()
b = open("test_api_result.expected.txt").readlines()
with open("tmp.html", "w") as outf:
    outf.write(difflib.HtmlDiff().make_file(a,b))

And the results: https://www.jefftk.com/html-diff-output-repro

I don't see these spurious deltas when running diff:

$ diff test_api_result.*
31,32c31,32
<             'latitude': 1,
<             'longitude': 1,
---
>             'latitude': 1.0,
>             'longitude': 1.0,
40c40
<         'meeting_url': '',
---
>         'meeting_url': None,
77,78c77,78
<             'latitude': 1,
<             'longitude': 1,
---
>             'latitude': 1.0,
>             'longitude': 1.0,
86c86
<         'meeting_url': '',
---
>         'meeting_url': None,
...

CPython versions tested on:

3.13

Operating systems tested on:

macOS

Start by reproducing the report with test_api_result.response.txt and test_api_result.expected.txt, then inspect the HtmlDiff output at the provided reproduction page and compare it with diff. The work is done when unchanged lines are no longer marked as changes while the actual differences remain visible.