pkgconfig.relocatable in subproject default_options fails in parent project setup

[seingierf]

Describe the bug
When setting up a parent project that includes a subproject with pkgconfig.relocatable=true in its default_options, meson setup fails in the parent project with the error:

subprojects/mysubprj/meson.build:1:0: ERROR: In subproject mysubprj: Unknown options: "mysubprj:pkgconfig.relocatable"

However, running meson setup directly within the subproject works without issue.
This change in behavior started with the following commit:

commit 6e200222957063819a00e3bf767ce28b7489c31f
Author: Jussi Pakkanen <jpakkane@gmail.com>
Date:   Sun Jul 14 19:33:41 2024 +0300

    Remove module type from OptionKey.

To Reproduce
In the parent project meson.build:

project('test', version : '1.0')
subproject('mysubprj')

In the subproject meson.build:

project('mysubprj', version : '1.0', default_options: ['pkgconfig.relocatable=true'])

Command-line steps:

cd test
meson setup build
# Error as shown above
cd test/subprojects/mysubprj
meson setup build
# Success

Expected behavior
The meson setup command in the parent project should successfully handle pkgconfig.relocatable=true in subproject default_options as it did in previous versions.

system parameters

• Is this a cross build or just a plain native build (for the same computer)?
  native
• what operating system (e.g. MacOS Catalina, Windows 10, CentOS 8.0, Ubuntu 18.04, etc.)
  Ubuntu 24.04
• what Python version are you using e.g. 3.8.0
  3.12.3
• what meson --version
  1.6.0

[amyspark]

Can confirm when using librsvg as a wrap from within the GStreamer repository.