fix: process completes with exit code 69 when warning occurs during test

[orestesgaolin]

Description

If warning occurs during running a test, the very_good test command exits with code 69

e.g. output from GitHub Action:

Run very_good test --coverage -x 'presubmit-only' --test-randomize-ordering-seed random
Running "flutter test" in /home/runner/work/org/repo...
Shuffling test order with --test-randomize-ordering-seed=2795804525
Optimizing tests (4.0s)

00:00 ...
00:01 ...
00:02 ...
00:03 ...
00:04 ...
00:05 ...
00:06 ...
00:07 .../opt/hostedtoolcache/.pub-cache/hosted/pub.dartlang.org/
cached_network_image-3.2.0/lib/src/image_provider/cached_network_image_provider.dart:109:29: 
Warning: Operand of null-aware operation '?.' has type 'PaintingBinding' which excludes null.

Error: Process completed with exit code 69.

The original warning in cached_network_image is already tracked here: Baseflow/flutter_cached_network_image#732. Nonetheless I think the warning should not fail the step.

Additional Context

Affects:

• very_good_cli 0.7.0
• Dart 2.17
• Flutter 3.0.0
• running on macOS and Ubuntu