Links to container images on Linux install page mention nightly instead of stable

[czechboy0]

Describe the bug

Links to container images on Linux install page mention nightly instead of stable.

For example on this page: https://www.swift.org/install/linux/ubi/9/ - the "Container" section has 6.2.1-nightly-rhel-ubi9 - but there's no reason for the nightly, I think, it should just say 6.2.1-rhel-ubi9.

Any mention of nightly builds should be under the Development Snapshots lower down the page, rather than in the top (implicitly "Production Snapshot") of the page.

To Reproduce

Visit https://www.swift.org/install/linux/ubi/9/
Check the Container section at the top.

Expected behavior

Should be 6.2.1-rhel-ubi9 (no nightly).

Actual behavior

Shows 6.2.1-nightly-rhel-ubi9.

[czechboy0]

I filed this issue to first verify with y'all that this is indeed a bug, and I'm happy to open a PR fixing it if so.