DOC: Convert v to conv_val in function for pytables.py

[migelogali]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

pandas\pandas\core\computation\pytables.py

Documentation problem

Many instances of just v in this function. Wanted to clarify throughout

Suggested fix for documentation

Change v to conv_val

[migelogali]

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