fix: Don't create dynamic property in Dispatcher

[TysonAndre]

trafficstars

https://wiki.php.net/rfc/deprecate_dynamic_properties causes this to emit an E_DEPRECATION notice and this will throw in PHP 9.0 unless subclasses happen to declare that property as protected/public

A private property was proposed because:

• This was undocumented and I assume unintentional.
• This will not conflict with any properties of the same name and different types (or readonly properties) in subclasses.

[codecov[bot]]

Codecov Report

Merging #56 (6a2482d) into master (b5f37db) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #56   +/-   ##
=========================================
  Coverage     89.07%   89.07%           
  Complexity       58       58           
=========================================
  Files             8        8           
  Lines           119      119           
=========================================
  Hits            106      106           
  Misses           13       13           

Impacted Files	Coverage Δ
lib/Dispatcher.php	88.88% <ø> (ø)