Memory goldens causing bot failures with 0.00% diffs

[kenzieschmoll]

example:

03:27 +244 ~3: /home/runner/work/devtools/devtools/packages/devtools_app/test/memory_screen_test.dart: MemoryScreen Chart Select Hover Test                                                            
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown while running async test code:
Golden "goldens/memory_hover_card.png": Pixel test failed, 0.00% diff detected.
Failure feedback can be found at
/home/runner/work/devtools/devtools/packages/devtools_app/test/failures

When the exception was thrown, this was the stack:
#0      LocalFileComparator.compare (package:flutter_test/src/_goldens_io.dart:101:7)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)
...
════════════════════════════════════════════════════════════════════════════════════════════════════

example bot run: https://github.com/flutter/devtools/pull/2931/checks?check_run_id=2421989219