Update dependency probot to v7.4.0

[renovate]

This PR contains the following updates:

Package	Type	Update	Change	References
probot	dependencies	minor	7.3.1 -> 7.4.0	homepage, source

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Release Notes

probot/probot

v7.4.0

Compare Source

Improvements

• Docs: #​739 @​bkeepers, #​740 @​JasonEtco, #​741 @​yeskunall, #​698 @​bdougie, #​734 @​hiimbex, #​756 @​hiimbex, #​752 @​TimonVS, #​773 @​matchai
• Tests/Typescript improvements: #​696 @​macklinu, #​704 @​macklinu, #​718 @​TimonVS, #​710 @​bobvanderlinden
• Version updates: #​750, #​768 @​gr2m - updating Octokit to v15.18
• Recent updates/Fixes:
  • Allow starting probot without token or id/cert (#​738) @​bkeepers
  • Do not require token on probot-receive (#​754) @​gimenete
  • Include version in manifest (#​763) @​wilhelmklopp
    See full changelog

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