[Fix] Add GPG keys in CI

[MeowZheng]

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Motivation

CI Installation is broken.
related pr open-mmlab/mmocr#988

Modification

Add libgl1-mesa-glx in system dependencies

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
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 test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMDet3D.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Merging #1532 (5ebf12a) into master (62c3a7d) will increase coverage by 0.10%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1532      +/-   ##
==========================================
+ Coverage   90.30%   90.40%   +0.10%     
==========================================
  Files         140      141       +1     
  Lines        8345     8443      +98     
  Branches     1403     1423      +20     
==========================================
+ Hits         7536     7633      +97     
- Misses        571      572       +1     
  Partials      238      238              

Flag	Coverage Δ
unittests	90.40% <ø> (+0.10%)	⬆️

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

Impacted Files	Coverage Δ
mmseg/core/__init__.py	100.00% <0.00%> (ø)
mmseg/core/utils/__init__.py	100.00% <0.00%> (ø)
mmseg/models/backbones/__init__.py	100.00% <0.00%> (ø)
mmseg/core/layer_decay_optimizer_constructor.py
...eg/core/utils/layer_decay_optimizer_constructor.py
...re/optimizers/layer_decay_optimizer_constructor.py	96.11% <0.00%> (ø)
mmseg/models/backbones/mae.py	91.83% <0.00%> (ø)
mmseg/core/optimizers/__init__.py	100.00% <0.00%> (ø)
mmseg/models/backbones/beit.py	93.12% <0.00%> (+1.29%)	⬆️

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