Docs: Preprocessor for Python < 3.12

[Lorak-mmk]

Preprocessor script was using syntax that works with Python 3.12 but not with older version.
Namely, string in format string using the same delimiter as outer string. Example: f'abc{'def'}xyz'

This commit changes delimiters of inner string to make script compatible with older versions of Python.

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• I added relevant tests for new features and bug fixes.
• All commits compile, pass static checks and pass test.
• PR description sums up the changes and reasons why they should be introduced.
• I have provided docstrings for the public items that I want to introduce.
• I have adjusted the documentation in ./docs/source/.
• I added appropriate Fixes: annotations to PR description.

[piodul]

Preprocessor script was using syntax that works with Python 3.12 but not with older version.

Why did the CI checks pass in the PR that introduced it, then? #910

As a side not, please also make sure to tick off the relevant boxes in the "Pre-review checklist". They are not optional for the maintainers.

[Lorak-mmk]

Preprocessor script was using syntax that works with Python 3.12 but not with older version.

Why did the CI checks pass in the PR that introduced it, then? #910

Preprocessor crash is not a hard error for documentation building - it will just build using unmodified sources.

[piodul]

Preprocessor script was using syntax that works with Python 3.12 but not with older version.

Why did the CI checks pass in the PR that introduced it, then? #910

Preprocessor crash is not a hard error for documentation building - it will just build using unmodified sources.

Yeah, looks like it, and it is already reported as a bug: rust-lang/mdBook#1872