Bump golang in /internal/witness/cmd/feeder (#1235)

Bumps golang from 1.21.3-bookworm to 1.21.4-bookworm.

---
updated-dependencies:
- dependency-name: golang
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

internal/witness/cmd/feeder/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.21.3-bookworm@sha256:5bafbbb109f02aaf6b41ddc19f54919773c3006f1cbda1599112603367642f0e as builder
+FROM golang:1.21.4-bookworm@sha256:85aacbed94a248f792beb89198649ddbc730649054b397f8d689e9c4c4cceab7 as builder
 
 ARG GOFLAGS=""
 ENV GOFLAGS=$GOFLAGS