Trigger immediate background fetch when switching repos

[stefanhaller]

If background fetching is on (which it is by default), we usually run the first background fetch right after opening lazygit, which is nice because it immediately fetches all the stuff that's new. However, when switching to a different repo from within lazygit (either with the recent repos menu or by going into or out of a submodule) we didn't do that, and you'd have to wait for the next regular background fetch to come along. I'm finding myself pressing f in the Files panel to manually fetch after entering a submodule, and I shouldn't have to do that.

This PR makes it so that when you switch repos, we trigger a background fetch immediately (unless the last one for this repo was less than the auto-fetch interval ago, in which case it's unnecessary).

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for ce762221	✅ 18.37%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (ce76222)	Report Missing	Report Missing	Report Missing
Head commit (2af56de)	59115	51394	86.94%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#5047)	49	9	18.37%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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Footnotes

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