Update golang Docker tag to v1.15.3 (master)

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
golang	final	patch	1.15.2 -> 1.15.3

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[codecov-io]

Codecov Report

Merging #1759 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1759   +/-   ##
=======================================
  Coverage   58.74%   58.74%           
=======================================
  Files          33       33           
  Lines        3624     3624           
=======================================
  Hits         2129     2129           
  Misses       1237     1237           
  Partials      258      258           

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