Use smtp.gmail.com as EMAIL_HOST

[Xpirix]

This PR is a fix for the email-sending feature since noreply@qgis.org goes sometimes in the spam folder.

Change summary:

• Use smtp.gmail.com as email host
• Replace noreply@qgis.org with automation@qgis.org

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 82.45%. Comparing base (32e0504) to head (5bfb1ca).

Files	Patch %	Lines
qgis-app/plugins/tests/test_plugin_update.py	66.66%	2 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           master     #356       +/-   ##
===========================================
+ Coverage   36.08%   82.45%   +46.37%     
===========================================
  Files         111      149       +38     
  Lines        4900     5933     +1033     
===========================================
+ Hits         1768     4892     +3124     
+ Misses       3132     1041     -2091     

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