ci: fixed broken ci

[lamweili]

fixed ci failing due to incompatible dev dependencies for Node.js <=12

• ci regression from 63340fa
  • chore(deps-dev): downgraded mocha from ^10.1.0 to ^6.2.3

[codecov-commenter]

Codecov Report

Merging #1753 (889e90c) into master (0769a85) will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1753      +/-   ##
==========================================
+ Coverage   94.36%   94.42%   +0.06%     
==========================================
  Files          14       14              
  Lines        1135     1148      +13     
==========================================
+ Hits         1071     1084      +13     
  Misses         64       64              

Impacted Files	Coverage Δ
src/request-base.js	93.06% <ø> (ø)
src/agent-base.js	100.00% <0.00%> (ø)
src/node/index.js	93.69% <0.00%> (+0.02%)	⬆️
src/utils.js	97.36% <0.00%> (+0.14%)	⬆️
src/node/http2wrapper.js	96.46% <0.00%> (+0.19%)	⬆️
src/node/agent.js	89.13% <0.00%> (+0.49%)	⬆️

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[lamweili]

@titanism, this would fix the broken ci tests by downgrading the mocha.
It is fine because it's a dev dependency anyway.

No release is needed as this doesn't affect the code.