Dependencies on a method name is not invoking

#### ALL software version info
param.__version__ : 1.13.0

#### Description of expected behavior and the observed behavior
Following the tutorial in the official reference
https://pyviz-dev.github.io/param/user_guide/Dependencies_and_Watchers.html#dependency-specs
Under dependency specs, it is stated that a method can depends on another method by another method's name.

However, cb4 does not execute after invoking cb3

#### Complete, minimal, self-contained example code that reproduces the issue

```
# code goes here between backticks
import param

class C(param.Parameterized):
_countries = {'Africa': ['Ghana', 'Togo', 'South Africa'],
'Asia' : ['China', 'Thailand', 'Japan', 'Singapore'],
'Europe': ['Austria', 'Bulgaria', 'Greece', 'Switzerland']}

continent = param.Selector(list(_countries.keys()), default='Asia')
country = param.Selector(_countries['Asia'])

@param.depends('continent', watch=True)
def _update_countries(self):
countries = self._countries[self.continent]
self.param['country'].objects = countries
if self.country not in countries:
self.country = countries[0]

c = C()

class D(param.Parameterized):
x = param.Number(7)
s = param.String("never")
i = param.Integer(-5)
o = param.Selector(['red', 'green', 'blue'])
n = param.ClassSelector(param.Parameterized, c, instantiate=False)

@param.depends('x', 's', 'n.country', 's:constant', watch=True)
def cb1(self):
print(f"cb1 x={self.x} s={self.s} "
f"param.s.constant={self.param.s.constant} n.country={self.n.country}")

@param.depends('n.param', watch=True)
def cb2(self):
print(f"cb2 n={self.n}")

@param.depends('x', 'i', watch=True)
def cb3(self):
print(f"cb3 x={self.x} i={self.i}")

@param.depends('cb3', watch=True)
def cb4(self):
print(f"cb4 x={self.x} i={self.i}")

d = D()
d
```

#### Stack traceback and/or browser JavaScript console output

#### Screenshots or screencasts of the bug in action

Changing d.x works as expected but calling d.cb3 does not invoke d.cb4