Fix typo (RDIR->SECDIR)

[yerbol-akhmetov]

Changes proposed in this Pull Request

Good day. This PR tends to fix the issue with input of build_clustered_population_layouts rule. gdp_layout needs to be stored in SECDIR as noted by @finozzifa, not RDIR. It was a type left from previous PR #1544. @davide-f

Checklist

• I consent to the release of this PR's code under the AGPLv3 license and non-code contributions under CC0-1.0 and CC-BY-4.0.
• I tested my contribution locally and it seems to work fine.
• A note for the release notes doc/release_notes.rst is amended in the format of previous release notes, including reference to the requested PR.

[davide-f]

Great catch @yerbol-akhmetov @finozzifa !
Merging