chore(docs): Fix the rendering of an expression in docstring

[martin-g]

Which issue does this PR close?

Closes N/A.

Rationale for this change

https://docs.rs/datafusion/latest/datafusion/catalog/trait.Session.html#tymethod.create_physical_expr renders:

Note: The expression is not simplified or otherwise optimized: `a = 1

* 2will not be simplified toa = 3` as this

What changes are included in this PR?

Keep the expression on one line.

What is the testing strategy for this PR?

Build the docs and verify that it renders well.

Are there any user-facing changes?

No.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.93%. Comparing base (606ae0f) to head (b935903).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25379      +/-   ##
==========================================
- Coverage   81.94%   81.93%   -0.02%     
==========================================
  Files        1135     1136       +1     
  Lines      428278   428677     +399     
  Branches   428278   428677     +399     
==========================================
+ Hits       350952   351230     +278     
- Misses      56369    56433      +64     
- Partials    20957    21014      +57     

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[martin-g]

Thank you for the review, @nuno-faria !