Update cloud_firestore dependency

[daniloapr]

Update the cloud_firestore dependency to resolve the following conflict.

Because fake_cloud_firestore 2.5.2 depends on cloud_firestore ^4.17.0 and no versions of fake_cloud_firestore match >2.5.2 <3.0.0, fake_cloud_firestore ^2.5.2 requires cloud_firestore ^4.17.0.
So, because [APP] depends on both cloud_firestore ^5.0.0 and fake_cloud_firestore ^2.5.2, version solving failed.

fake_cloud_firestore: ^2.5.2
cloud_firestore: ^5.0.0

[atn832]

Just published version 3.0.0. https://pub.dev/packages/fake_cloud_firestore/changelog#300