Make formatting of enums in py3.11 consistent with earlier Python ver…

…sions (#550)

Python 3.11 changes the behavior of  `enum.Enum.__format__()` slightly. f-strings (and a few other string formatting methods) rely on dunder method `__format___()`. This change makes the formatting of enums as strings consistent
among all supported Python versions.

Fixes #447

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Change log
 
+- [#447](https://github.com/mobilityhouse/ocpp/issues/447) Make formatting of enums in py3.11 consistent with earlier Python versions
 - [#421](https://github.com/mobilityhouse/ocpp/issues/421) Type of v16.datatypes.SampledValue.context is incorrect 
 
 ## 0.25.0 (2024-01-08)
@@ -13,6 +14,7 @@
 
 ## 0.24.0 (2023-12-07)
 
+
 - [#539](https://github.com/mobilityhouse/ocpp/issues/539) feat: Add ChargePoint._handle_call return value. Thanks [@wafa-yah](https://github.com/wafa-yah)
 - [#266](https://github.com/mobilityhouse/ocpp/issues/266) fix: Central System documentation link.
 - [#516](https://github.com/mobilityhouse/ocpp/issues/516) OCPP 2.0.1 add additional security events from v1.3.