Update golang Docker tag to v1.16.4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
golang	docker	patch	1.16.3-stretch -> 1.16.4-stretch

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[codecov-commenter]

Codecov Report

Merging #59 (f59f459) into master (c9340b2) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #59   +/-   ##
=======================================
  Coverage   69.04%   69.04%           
=======================================
  Files           1        1           
  Lines          84       84           
=======================================
  Hits           58       58           
  Misses         15       15           
  Partials       11       11           

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