BuildDiff: make actual hash ref

Dependencies

• [2] NYIIFA32 BuildDiff: split out from JobsetEval GET impl
• [3] 3R3AYTCQ t/BuildDiff: init

Change contents

• replacement in src/lib/Hydra/Helper/BuildDiff.pm at line 21
  [2.406]→[2.406:422](∅→∅)
  − my $ret = [
  [2.406]

  [2.422]
  + my $ret = {
• replacement in src/lib/Hydra/Helper/BuildDiff.pm at line 31
  [2.637]→[2.637:644](∅→∅)
  − ];
  [2.637]

  [2.644]
  + };
• replacement in t/Helper/BuildDiff.t at line 12
  [3.174]→[3.174:189](∅→∅)
  − is($ret, [
  [3.174]

  [3.189]
  + is($ret, {
• replacement in t/Helper/BuildDiff.t at line 22
  [3.404]→[3.404:412](∅→∅)
  − ]);
  [3.404]

  [3.412]
  + });