Add auto mode for pytest

[chillipeper]

Description

Starting from pytest-asyncio>=0.17, three modes are provided: auto,
strict, and legacy. Starting from pytest-asyncio>=0.19 the strict
mode is the default.

This is causing tests to fail when the latest version pytest-asyncio is installed

https://github.com/pytest-dev/pytest-asyncio/releases/tag/v0.19.0

Also removing the duplicate entry of dialogflow which is also making the tests fail

Status

READY

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Yes tests pass now

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

Merging #1942 (b902e31) into master (299cd55) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1942   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files          83       83           
  Lines        5354     5357    +3     
=======================================
+ Hits         5321     5324    +3     
  Misses         33       33           

Impacted Files	Coverage Δ
opsdroid/web.py	100.00% <100.00%> (ø)

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[FabioRosado]

Thanks! I've been thinking about doing this for a long time haha