Update dependency axllent/mailpit to v1.21.7

[renovate]

This PR contains the following updates:

Package	Update	Change
axllent/mailpit	patch	1.21.6 -> 1.21.7

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Release Notes

axllent/mailpit (axllent/mailpit)

v1.21.7

Compare Source

Chore

• Update node dependencies
• Update Go dependencies
• Bump Go version for automated testing
• Move smtpd & pop3 modules to internal
• Stricter SMTP 'MAIL FROM' & 'RCPT TO' handling (#​409)
• Display "To" details in mobile messages list
• Display "From" details in message sidebar (desktop) (#​403)

Fix

• Ignore unsupported optional SMTP 'MAIL FROM' parameters (#​407)
• Prevent splitting multi-byte characters in message snippets (#​404)

Testing

• Add smtpd tests

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