Add missing "disabler" kwarg to python.dependency()

There is a unit test using it and now fails because the warning about
unknown kwarg became fatal.

docs/markdown/Python-module.md

@@ -112,6 +112,8 @@ following keyword argument:
 - `embed`: *(since 0.53.0)* If true, Meson will try to find a python
   dependency that can be used for embedding python into an
   application.
+- `disabler` *(since 0.60.0)*: if `true` and the dependency couldn't be found,
+  returns a [disabler object](#disabler-object) instead of a not-found dependency.
 
 **Returns**: a [python dependency][`python_dependency` object]
 

mesonbuild/modules/python.py

@@ -458,6 +458,7 @@ class PythonInstallation(ExternalProgramHolder):
 
         return self.interpreter.func_shared_module(None, args, kwargs)
 
+    @disablerIfNotFound
     @permittedKwargs(permitted_dependency_kwargs | {'embed'})
     @FeatureNewKwargs('python_installation.dependency', '0.53.0', ['embed'])
     @noPosargs