[Fix] Update required xtcocotools version to v1.12

[ly015]

Motivation

Update required xtcocotools version to v1.12, which fixed a bug reported in #1280 .

Modification

BC-breaking (Optional)

Use cases (Optional)

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit tests to ensure correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Merging #1308 (76ac6c4) into master (2ea8ee6) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1308   +/-   ##
=======================================
  Coverage   84.10%   84.10%           
=======================================
  Files         215      215           
  Lines       17674    17674           
  Branches     3139     3139           
=======================================
+ Hits        14864    14865    +1     
  Misses       2018     2018           
+ Partials      792      791    -1     

Flag	Coverage Δ
unittests	84.03% <ø> (ø)

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Impacted Files	Coverage Δ
mmpose/datasets/pipelines/shared_transform.py	81.57% <0.00%> (+0.43%)	⬆️

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