fix(build): Incorrect package used for GPG

[khvn26]

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Changes

This fixes gpg not being available to the SaaS Docker image build:

 > [saas-api 1/4] RUN --mount=type=secret,id=sse_pgp_pkey   apk add gnupg &&   gpg --import /run/secrets/sse_pgp_pkey &&   mv /root/.gnupg/ /app/ &&   chown -R nobody /app/.gnupg/:
#0 0.745 (1/1) Installing gnupg (2.2.41-r2)
#0 0.934 OK: 76 MiB in 32 packages
#0 0.976 /bin/sh: gpg: not found
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https://github.com/Flagsmith/flagsmith/actions/runs/9990074115/job/27609995476

How did you test this code?

Ran docker build --target saas-api . locally.

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3 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
docs	⬜️ Ignored (Inspect)			Jul 18, 2024 10:53am
flagsmith-frontend-preview	⬜️ Ignored (Inspect)			Jul 18, 2024 10:53am
flagsmith-frontend-staging	⬜️ Ignored (Inspect)			Jul 18, 2024 10:53am

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-4355	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-e2e:pr-4355	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-4355	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-api:pr-4355	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-4355	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-4355	Finished ✅	Results ✅