automation: Update mastodon Docker tag to v4.1.6

This MR contains the following updates:

Package	Update	Change
mastodon	patch	4.1.5 -> 4.1.6

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Release Notes

mastodon/mastodon (mastodon)

v4.1.6

Compare Source

Fixed

• Fix memory leak in streaming server (ThisIsMissEm)
• Fix wrong filters sometimes applying in streaming (ClearlyClaire, ThisIsMissEm, renchap)
• Fix incorrect connect timeout in outgoing requests (ClearlyClaire)

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