rpcd-mod-rrdns/luci: lower cmake_minimum_required to 3.13

[Yepday]

Pull request details

Description

These packages only use basic CMake directives available since 2.x.
Requiring VERSION 3.31 breaks builds on common environments like
Ubuntu 22.04 which ships CMake 3.26.

Maintainer (preferred)

@jow-

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Tested on

OpenWrt version: OpenWrt 23.05-SNAPSHOT

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Checklist

• This PR is not from my main or master branch 💩, but a separate branch. ✅
• Each commit has a valid ✒️ Signed-off-by: Yepday <365256281@qq.com> row (via git commit --signoff).
• Each commit and PR title has a valid 📝 <package name>: title first line subject for packages.
• Incremented 🆙 any PKG_VERSION in the Makefile.

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Commit a1b1c48

• 🔶 Author name must be either a real name 'firstname lastname' or a nickname/alias/handle
  Actual: Yepday seems to be a nickname or an alias
  Expected: a real name 'firstname lastname'
• 🔶 Commit(ter) name must be either a real name 'firstname lastname' or a nickname/alias/handle
  Actual: Yepday seems to be a nickname or an alias
  Expected: a real name 'firstname lastname'

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