Handle the case when ~/.gradle does not exist

[snazy]

... for example when GitHub expired the Gradle cache.

As here: https://github.com/projectnessie/cel-java/runs/5973722511?check_suite_focus=true

[codecov]

Codecov Report

Merging #155 (a5b6b8d) into main (40c88bf) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #155   +/-   ##
=========================================
  Coverage     80.37%   80.37%           
  Complexity     1835     1835           
=========================================
  Files           100      100           
  Lines          7899     7899           
  Branches       1143     1143           
=========================================
  Hits           6349     6349           
  Misses         1033     1033           
  Partials        517      517           

Flag	Coverage Δ
java	80.37% <ø> (ø)

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