Update oven/bun Docker tag to v1.4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
oven/bun	final	minor	1.3-slim → 1.4-slim
oven/bun	stage	minor	1.3-slim → 1.4-slim

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[ecv]

Closing under the shared dependency dashboard gate. Nothing reopens on its own now. Take this update by ticking it on the dependency dashboard whenever it is wanted.

[renovate]

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