Fix _create_synth_dataset when MMM has no controls

[PabloRoque]

Description

MMM._create_synth_dataset does not work in MMMs without controls.

Note the underscore difference.

Before:

        if controls is not None:
            _controls: list[str] = controls
        else:
            controls = []

After:

        if controls is not None:
            _controls: list[str] = controls
        else:
            _controls = [] 

Added a test and fixtures to test the method in MMMs without controls in the future.

Related Issue

• Closes budget allocation with no control vars #1030,

Checklist

• Checked that the pre-commit linting/style checks pass. Feel free to comment pre-commit.ci autofix to auto-fix.
• Included tests that prove the fix is effective or that the new feature works

---

📚 Documentation preview 📚: https://pymc-marketing--1513.org.readthedocs.build/en/1513/

[wd60622]

There is an issue for this. Can you link

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.74%. Comparing base (26e80c0) to head (0ff9fcc).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pymc_marketing/mmm/mmm.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1513   +/-   ##
=======================================
  Coverage   92.74%   92.74%           
=======================================
  Files          52       52           
  Lines        6120     6123    +3     
=======================================
+ Hits         5676     5679    +3     
  Misses        444      444           

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[PabloRoque]

There is an issue for this. Can you link

I was not aware of the opened issue. Linked now.

[wd60622]

Awesome. Thanks!