[Enhancement] Modify MMCV version requirement

[xiexinch]

Modification

• MMCV_MAX: 1.6.0 -> 1.7.0
• mmcv_verion <= mmcv_max_version --> mmcv_version < mmcv_max_version

[codecov]

Codecov Report

Merging #1764 (ac26977) into master (8556944) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1764   +/-   ##
=======================================
  Coverage   89.04%   89.04%           
=======================================
  Files         144      144           
  Lines        8636     8636           
  Branches     1458     1458           
=======================================
  Hits         7690     7690           
  Misses        706      706           
  Partials      240      240           

Flag	Coverage Δ
unittests	89.04% <100.00%> (ø)

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

Impacted Files	Coverage Δ
mmseg/__init__.py	90.32% <100.00%> (ø)

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