fix: use flexbox instead of font-size to ensure the icon is centered … #4964

Job	Run time
build	3m 50s
setup-matrix	3s
test	2m 10s
lint	3m 29s
e2e (1, ../ui/collections/forms/src/CheckboxFieldFF/features/can_toggle_a_boolean.feature, ../ui/...	5m 30s
e2e (2, ../ui/collections/forms/src/CheckboxFieldFF/features/can_toggle_a_value.feature, ../ui/co...	4m 51s
e2e (3, ../ui/collections/forms/src/CheckboxFieldFF/features/displays_error.feature, ../ui/collec...	5m 4s
e2e (4, ../ui/collections/forms/src/FileInputFieldFF/features/accepts_file.feature, ../ui/collect...	4m 56s
e2e (5, ../ui/collections/forms/src/FileInputFieldFF/features/displays_error.feature, ../ui/colle...	5m 18s
e2e (6, ../ui/collections/forms/src/InputFieldFF/features/can_set_a_value.feature, ../ui/collecti...	5m 27s
e2e (7, ../ui/collections/forms/src/InputFieldFF/features/displays_error.feature, ../ui/collectio...	4m 54s
publish	9m 25s
	54m 57s

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