fix: code block indenting and fencing

[plaindocs]

Description

Fixes broken code blocks

Related Issue(s)

For example:

• closes [Docs]: usage/appending-overwriting-delta-lake-table has broken language tabs #4200

Documentation

NA. I didn't check the code, just the broken display issue.

[github-actions]

ACTION NEEDED

delta-rs follows the Conventional Commits specification for release automation.

The PR title and description are used as the merge commit message. Please update your PR title and description to match the specification.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.81%. Comparing base (b5bd6ac) to head (35d0265).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4212      +/-   ##
==========================================
- Coverage   76.82%   76.81%   -0.02%     
==========================================
  Files         166      166              
  Lines       48231    48209      -22     
  Branches    48231    48209      -22     
==========================================
- Hits        37053    37031      -22     
- Misses       9319     9320       +1     
+ Partials     1859     1858       -1     

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[plaindocs]

Just noticed that this should probably declare import pandas as pd or use vanilla python.