Resolve "Release image job fails: E: Unable to locate package python3-docutil"

What does this Merge Request do and why?

This MR fixes a typo (introduced in !2344 (diffs, comment 805810247)) to allow Debian users to run gdk update without seeing the following error:

E: Unable to locate package python3-docutil

See #1402 (closed)

Merge Request checklist

• [-] This change is backward compatible. If not, please include steps to communicate to our users.
• [-] Tests added for new functionality. If not, please raise Issue to follow-up.
• [-] Documentation added/updated, if needed.
• [-] gdk doctor test added, if needed.
• [-] Add the ~highlight label if this MR should be included in the CHANGELOG.md.

Closes #1402 (closed)