Update mobilecoin/builder-install Docker tag to v0.0.21

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
mobilecoin/builder-install	container	patch	v0.0.20 -> v0.0.21

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[codecov-commenter]

Codecov Report

Base: 59.50% // Head: 59.50% // No change to project coverage 👍

Coverage data is based on head (755ef03) compared to base (aefff76).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #620   +/-   ##
========================================
  Coverage    59.50%   59.50%           
========================================
  Files           83       83           
  Lines        11540    11540           
  Branches      1867     1867           
========================================
  Hits          6867     6867           
  Misses        3124     3124           
  Partials      1549     1549           

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