Catch 'Error in reactor loop escaped: mode not supported for this object: r'

[MSP-Greg]

Description

The following error happens intermittently in non MRI CI:

Error in reactor loop escaped: mode not supported for this object: r (ArgumentError)

PR adds a rescue in `Reactor#register.

Note that #2432 also attempted to catch this (without a rescue), but some errors still occur. I tried to remove it, and doing so caused more intermittent errors...

Updated HISTORY.md

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• I have added an entry to History.md if this PR fixes a bug or adds a feature. If it doesn't need an entry to HISTORY.md, I have added [changelog skip] or [ci skip] to the pull request title.
• I have added appropriate tests if this PR fixes a bug or adds a feature.
• My pull request is 100 lines added/removed or less so that it can be easily reviewed.
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• I have updated the documentation accordingly.
• All new and existing tests passed, including Rubocop.

[nateberkopec]

I think you're gonna wanna avoid doing so many changes to History.md on your PRs, gonna make them impossible to merge.

Otherwise LGTM, merge it yourself I think.