[openstreetmap/openstreetmap-website] Bump mini_magick from 4.9.3 to 4.9.4 (#2325)

[dependabot[bot]]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting `@dependabot ignore this major version` or `@dependabot ignore this minor version`.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.

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