RCORE-2264: Skip backup files when scanning for audit Realms to upload

[tgoyne]

Backup realms from file format upgrades are placed next to the original file, so the audit realm pool will find the backup and attempt to upload it, triggering another upgrade and backup until the filename becomes too long and it crashes instead. It needs to instead skip the backup files and delete any lingering backups of Realms which have already been uploaded.

Fixes #8040

[coveralls-official]

Pull Request Test Coverage Report for Build thomas.goyne_526

Details

• 38 of 43 (88.37%) changed or added relevant lines in 3 files are covered.
• 68 unchanged lines in 9 files lost coverage.
• Overall coverage increased (+0.007%) to 91.116%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/realm/object-store/audit.mm	26	31	83.87%

Files with Coverage Reduction	New Missed Lines	%
src/realm/sync/network/websocket.cpp	1	72.2%
src/realm/sync/noinst/server/server_history.cpp	1	62.92%
src/realm/sync/transform.cpp	3	61.01%
test/fuzz_group.cpp	3	47.05%
src/realm/table.cpp	4	90.42%
src/realm/sync/noinst/server/server.cpp	6	74.17%
src/realm/index_string.cpp	8	84.85%
src/realm/sync/instruction_applier.cpp	15	68.01%
src/realm/object-store/audit.mm	27	90.98%

Totals
Change from base Build 2615:	0.007%
Covered Lines:	217220
Relevant Lines:	238400

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💛 - Coveralls

[jedelbo]

LGTM