Bump pymdown-extensions from 10.12 to v10.13

[dghubble-renovate]

This PR contains the following updates:

Package	Update	Change
pymdown-extensions	minor	==10.12 -> ==10.13

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Release Notes

facelessuser/pymdown-extensions (pymdown-extensions)

v10.13

Compare Source

10.13

• NEW: Snippets: Allow multiple line numbers or line number blocks separated by ,.
• NEW: Snippets: Allow using a negative index for number start indexes and end indexes. Negative indexes are converted to positive indexes based on the number of lines in the snippet.
• FIX: Snippets: Properly capture empty newline at end of file.
• FIX: Snippets: Fix issue where when non sections of files are included, section labels are not stripped.
• FIX: BetterEm: Fixes for complex cases.
• FIX: Blocks: More consistent handling of empty newlines in block processor extensions.

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