build(deps): bump swift in /apps/headless (#97)

Bumps swift from 6.1-bookworm to 6.3-bookworm.

---
updated-dependencies:
- dependency-name: swift
  dependency-version: 6.3-bookworm
  dependency-type: direct:production
...

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

Author: dependabot[bot]

apps/headless/Dockerfile.linux

@@ -1,4 +1,4 @@
-FROM swift:6.1-bookworm AS builder
+FROM swift:6.3-bookworm AS builder
 WORKDIR /src
 COPY Package.swift ./
 COPY main.swift ./