fix: allow returning none for generic bindings

[hallvictoria]

Description

Currently, when a function is triggered, the worker expects a request body with the trigger. However, in the case of generic binding types like the Dapr Cron binding trigger, no data is sent with the trigger request. This causes the worker to crash with an exception AttributeError: 'NoneType' object has no attribute 'type'. This fix enables triggers to execute successfully even if the trigger calls the app without any request body.

As per 1391, implicit output is enabled for generic types. Therefore, function apps with generic bindings that are also returning None will face an error TypeError: unable to encode outgoing TypedData: unsupported type "<class 'azure_functions_worker.bindings.generic.GenericBinding'>" for Python type "NoneType". This changes the worker to allow this scenario.

Fixes #1316
Fixes #1479

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.46%. Comparing base (7de7724) to head (dff0911).
Report is 3 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1379      +/-   ##
==========================================
+ Coverage   85.44%   85.46%   +0.01%     
==========================================
  Files          35       35              
  Lines        1965     1967       +2     
  Branches      370      371       +1     
==========================================
+ Hits         1679     1681       +2     
  Misses        213      213              
  Partials       73       73              

Flag	Coverage Δ
unittests	85.40% <100.00%> (+0.01%)	⬆️

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[vrdmr]

nit; otherwise LGTM

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 85.12%. Comparing base (330783f) to head (40c105b).
Report is 5 commits behind head on dev.

❗ Current head 40c105b differs from pull request most recent head ca87969. Consider uploading reports for the commit ca87969 to get more accurate results

Files	Patch %	Lines
azure_functions_worker/bindings/generic.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1379      +/-   ##
==========================================
+ Coverage   84.64%   85.12%   +0.48%     
==========================================
  Files          35       35              
  Lines        2052     2004      -48     
  Branches      387      381       -6     
==========================================
- Hits         1737     1706      -31     
+ Misses        232      223       -9     
+ Partials       83       75       -8     

Flag	Coverage Δ
unittests	85.07% <75.00%> (+0.47%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

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