`meson subprojects update` doesn't initialize new submodules

[seishun]

Describe the bug
If after updating a Git subproject the repository has any submodules that it didn't before updating, they aren't initialized.

To Reproduce

subprojects/wxWidgets.wrap (before)

[wrap-git]
directory = wxWidgets
url = https://github.com/wxWidgets/wxWidgets.git
revision = v3.1.4
clone-recursive = true

1. meson subprojects download

subprojects/wxWidgets.wrap (after)

[wrap-git]
directory = wxWidgets
url = https://github.com/wxWidgets/wxWidgets.git
revision = v3.2.2
clone-recursive = true

2 meson subprojects update
3. cd subprojects/wxWidgets
4. git submodule status

Expected behavior
New submodules are initialized.

system parameters

• Python 3.13.1
• meson 1.7.0 and HEAD