DOC: update CI environment dependencies for doc build

[Dawnfz-Lenfeng]

What do these changes do?

• Updated the doc build environment dependencies, separating them from other module dependencies.
• Handled the absence of lightgbm by setting import lightgbm to None, preventing import errors when it's not installed.

Related issue number

Fixes #xxxx

Check code requirements

• tests added / passed (if needed)
• Ensure all linting tests pass

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.97%. Comparing base (c765e57) to head (aecfb9f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #814   +/-   ##
=======================================
  Coverage   82.97%   82.97%           
=======================================
  Files        1070     1070           
  Lines       80031    80033    +2     
  Branches    16528    16529    +1     
=======================================
+ Hits        66406    66410    +4     
+ Misses      12030    12023    -7     
- Partials     1595     1600    +5     

Flag	Coverage Δ
unittests	82.88% <ø> (+<0.01%)	⬆️

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