Fix: update the version in the specs for Kong Admin 3.9

[lena-larionova]

Description

The 3.9 specs still list 3.8 as their version.

This is already fixed in Konnect Dev Portal, and there's a parallel PR open on docs.konghq.com.

Relates to Kong/docs.konghq.com#8418.

Preview Links

Checklist

• Every page is page one.
• Tested how-to docs. If not, note why here.
• All pages contain metadata.
• Updated sources.yaml. For more info, review track docs changes
• Any new docs link to existing docs.
• All autogenerated instructions render correctly (API, decK, Konnect, Kong Manager).
• Style guide (capitalized gateway entities, placeholder URLs) implemented correctly.

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[lena-larionova]

Closing, I forgot we had an action to do this automatically.