fix mmseg out_channels=1

[RunningLeon]

Motivation

Fix #2161

Modification

Please briefly describe what modification is made in this PR.

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

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit tests to ensure the correctness.
3. If the modification has a dependency on downstream projects of a newer version, this PR should be tested with all supported versions of downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Patch coverage: 88.23% and project coverage change: +0.03 🎉

Comparison is base (a8775d2) 49.81% compared to head (392cc38) 49.85%.

❗ Current head 392cc38 differs from pull request most recent head d4cc6f4. Consider uploading reports for the commit d4cc6f4 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2179      +/-   ##
==========================================
+ Coverage   49.81%   49.85%   +0.03%     
==========================================
  Files         341      341              
  Lines       13033    13036       +3     
  Branches     1910     1911       +1     
==========================================
+ Hits         6493     6499       +6     
+ Misses       6089     6086       -3     
  Partials      451      451              

Flag	Coverage Δ
unittests	49.85% <88.23%> (+0.03%)	⬆️

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

Impacted Files	Coverage Δ
...mmseg/models/segmentors/cascade_encoder_decoder.py	18.18% <0.00%> (+1.51%)	⬆️
mmdeploy/codebase/mmseg/models/segmentors/base.py	87.09% <92.85%> (+2.88%)	⬆️
...odebase/mmseg/models/segmentors/encoder_decoder.py	100.00% <100.00%> (+12.50%)	⬆️

... and 1 file with indirect coverage changes

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[grimoire]

LGTM