textcode markup: fix SyntaxWarning in regex

[gotmax23]

Tasks

• Reviewed contribution guidelines
• PR is descriptively titled 📑 and links the original issue above
• Tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR
  Run tests locally to check for errors.
• Commits are in uniquely-named feature branch and has no merge conflicts 📁
• Updated documentation pages (if applicable)
• Updated CHANGELOG.rst (if applicable)

[pombredanne]

Thanks!

[pombredanne]

Merging and ignoring Azure Ci heisenbug:

              ERROR: Unknown error:
E               Traceback (most recent call last):
E                 File "/home/vsts/work/1/s/src/scancode/interrupt.py", line 89, in interruptible
E                   create_signal(SIGALRM, handler)
E                 File "/opt/hostedtoolcache/Python/3.12.6/x64/lib/python3.12/signal.py", line 58, in signal
E                   handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))
E                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E               ValueError: signal only works in main thread of the main interpreter

[gotmax23]

Thanks!