[Fix] Fix num_images_per_prompt in controlnet

[LeoXing1996]

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Motivation

Related to #1927

Modification

If number control is 1, the control will be repeated for num_images_per_prompt * len(prompt) times.
Otherwise the number control must equal to number of prompt, and will be repeated for num_images_per_prompt times.

Unit tests are revised as well.

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

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Before PR:

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[codecov]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.01 ⚠️

Comparison is base (71d4195) 82.59% compared to head (f100531) 82.59%.

❗ Current head f100531 differs from pull request most recent head 89a5e7b. Consider uploading reports for the commit 89a5e7b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1936      +/-   ##
==========================================
- Coverage   82.59%   82.59%   -0.01%     
==========================================
  Files         413      413              
  Lines       27811    27812       +1     
  Branches     4366     4366              
==========================================
- Hits        22971    22970       -1     
+ Misses       3895     3893       -2     
- Partials      945      949       +4     

Flag	Coverage Δ
unittests	82.59% <50.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmagic/models/editors/controlnet/controlnet.py	47.36% <50.00%> (-0.46%)	⬇️

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[zengyh1900]

lgtm.