Fix gradle heap size configs

[cgtz]

Previously, we were increasing the heap size for the gradle daemon
but not for the test runner. This commit fixes that.

[codecov-io]

Codecov Report

Merging #1238 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1238   +/-   ##
=========================================
  Coverage     88.92%   88.92%           
  Complexity       60       60           
=========================================
  Files             6        6           
  Lines           352      352           
  Branches         37       37           
=========================================
  Hits            313      313           
  Misses           29       29           
  Partials         10       10

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