Throw if the main argument in plurals does not match the argument list.

[mosuem]

Fixes internal bug.
cc @Caffeinix

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Package publishing

Package	Version	Status	Publish tag (post-merge)
package:intl_translation	0.20.1	ready to publish	intl_translation-v0.20.1
package:intl	0.20.0-wip	WIP (no publish necessary)
package:intl4x	0.9.2-wip	WIP (no publish necessary)
package:messages	0.2.0	already published at pub.dev
package:messages_builder	0.2.1	already published at pub.dev
package:messages_serializer	0.2.1	already published at pub.dev
package:messages_shrinker	0.2.2-wip	WIP (no publish necessary)

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[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
intl_translation	None	0.20.1-wip	0.20.1	0.20.1	✔️

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File	Coverage
pkgs/intl_translation/lib/src/messages/submessages/submessage.dart	💚 62 %
pkgs/intl_translation/lib/visitors/plural_gender_visitor.dart	💚 13 %

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intl_translation	Message MainMessage

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Package	Version	Status
package:intl_translation	0.20.1	ready to publish
package:intl	0.20.0-wip	WIP (no publish necessary)
package:intl4x	0.9.2-wip	WIP (no publish necessary)
package:messages	0.2.0	already published at pub.dev
package:messages_builder	0.2.1	already published at pub.dev
package:messages_serializer	0.2.1	already published at pub.dev
package:messages_shrinker	0.2.2-wip	WIP (no publish necessary)

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