Pinecone test image - Explicitly select Alpine golang image

[Arkaniad]

I've noticed when trying to build the Dendrite Pinecone test image, the build fails due to apk not being available:

Checking out the Docker Hub repo for the golang image it looks like this can resovle to 1.22-bookworm, so this should ensure we get an Alpine-based image for this build.

Pull Request Checklist

• [x] I have added Go unit tests or Complement integration tests for this PR or I have justified why this PR doesn't need tests
• [x] Pull request includes a sign off below using a legally identifiable name or I have already signed off privately

Signed-off-by: Rhea Danzey <rdanzey@element.io>