Fix invocations of read_channel_metadata_from_db_file to expect a dict

[rtibbles]

Summary

• Fixes regressions introduced by Postgresql database import speedup #6115

References

Fixes #8251

Reviewer guidance

Can you now export to an external drive?

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[radinamatic]

Export to an USB drive is now working again on Windows 10, although somewhat more slowly than I remember... 🤔
logs.zip

@pcenov Could you confirm that exporting to external drive is working on Linux too, before we approve and merge? Thank you!

[pcenov]

@radinamatic I confirm that export and import to external drive is now working in both Linux and Windows.

[radinamatic]

Thank you, @pcenov! 👍🏽
I also managed to export from my dev VM, this should be good to go 💯

[radinamatic]

QA team says

[indirectlylit]

Is the inconsistency in getter style because some of these are supposed to throw value errors and others are supposed to return None if the items doesn't exist?

(Mainly just curious if this is part of an implicit required/optional API of some kind)

[rtibbles]

As it was 'like that when I got here' at this point, I am inferring - but I think these use of get versus direct key access is a result of newer fields being added that might be undefined in historic channel DB schema.