qt_import_plugins(target INCLUDE_BY_TYPE type) doesn't have any effect

How to reproduce

Use a static desktop build of Qt.
Take a Qt example that doesn't use Qt::PrintSupport.
I've used the easing widgets example.

Add PrintSupport to the find_package call:

find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets PrintSupport)

After creating the target executable, add the following:

qt_import_plugins(easing INCLUDE Qt6::QCupsPrinterSupportPlugin)

Configure the project with CMake and inspect the build.ninja file:

$ rg /plugins/printsupport < build.ninja
.../qtbase/plugins/printsupport/libcupsprintersupport.a
...

OK, this is fine. The plugin is linked.

Now, replace the qt_import_plugins call with

qt_import_plugins(easing INCLUDE_BY_TYPE printsupport)

and inspect build.ninja again.

Outcome: We don't link against libcupsprintersupport.a but we should.