chore: Lint fixes

[dnys1]

Issue #, if available:

Description of changes:

• Fixes and changes needed to support analysis under Dart 2.17 and pkg:lints 2.0

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[codecov-commenter]

Codecov Report

Merging #1471 (db3c12a) into main (8f862b3) will increase coverage by 0.17%.
The diff coverage is 45.25%.

@@            Coverage Diff             @@
##             main    #1471      +/-   ##
==========================================
+ Coverage   46.64%   46.82%   +0.17%     
==========================================
  Files         259      259              
  Lines       10153    10142      -11     
==========================================
+ Hits         4736     4749      +13     
+ Misses       5417     5393      -24     

Flag	Coverage Δ
android-unit-tests	∅ <ø> (∅)
flutter-unit-tests	37.00% <45.25%> (+0.21%)	⬆️
ios-unit-tests	85.12% <ø> (ø)

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Impacted Files	Coverage Δ
...y_api/lib/src/graphql/graphql_request_factory.dart	95.12% <ø> (+1.52%)	⬆️
..._api/lib/src/graphql/graphql_response_decoder.dart	93.75% <ø> (+8.03%)	⬆️
...plify_authenticator/lib/amplify_authenticator.dart	0.00% <0.00%> (ø)
...ator/lib/src/mixins/authenticator_phone_field.dart	0.00% <0.00%> (ø)
...ator/lib/src/mixins/authenticator_radio_field.dart	0.00% <0.00%> (ø)
...idgets/form_fields/confirm_sign_in_form_field.dart	4.06% <0.00%> (ø)
...ib/src/widgets/form_fields/phone_number_field.dart	0.00% <0.00%> (ø)
...widgets/form_fields/reset_password_form_field.dart	6.34% <0.00%> (ø)
...ib/src/widgets/form_fields/sign_up_form_field.dart	4.49% <0.00%> (ø)
...rc/widgets/form_fields/verify_user_form_field.dart	24.39% <0.00%> (ø)
... and 34 more