Persist schema version 7

[schmidt-sebastian]

Unlike all other migrations, we do not persist that we have migrated to version 7. This means we run the migration over and over again.

Fixes #8791

[google-oss-bot]

Coverage Report

Affected SDKs

• FirebaseFirestore-iOS-FirebaseFirestore.framework

  SDK overall coverage changed from 87.77% (121f56e) to 87.67% (ab4d3dc) by -0.10%.

  Filename	Base (121f56e)	Head (ab4d3dc)	Diff
  exception.cc	73.68%	23.68%	-50.00%
  exception_apple.mm	58.62%	89.66%	+31.03%
  leveldb_key.cc	97.84%	98.30%	+0.46%
  leveldb_migrations.cc	92.28%	92.31%	+0.03%
  leveldb_opener.cc	76.81%	74.64%	-2.17%
  ordered_code.cc	92.18%	90.14%	-2.04%
  serializer.cc	87.97%	87.65%	-0.33%
  watch_stream.cc	90.70%	95.35%	+4.65%
  write_stream.cc	94.37%	90.14%	-4.23%

Test Logs

• Base (121f56e9): https://github.com/firebase/firebase-ios-sdk/actions/runs/1370063638
• Head (ab4d3dc4): https://github.com/firebase/firebase-ios-sdk/actions/runs/1371379055