Improved compatibility with Python 3.5+ - Convert signal.SIGTERM to int

[phill84]

Solves the issue #9202

File changed: airflow/utils/process_utils.py

Problem
Since python3.5, signals have become IntEnum instead of int, therefore str(signal.SIGTERM) yields the string literal signal.SIGTERM instead of 15.

Solution
convert signal.SIGTERM to int first and then str

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[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contribution Guide (https://github.com/apache/airflow/blob/master/CONTRIBUTING.rst)
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[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[mik-laj]

@phill84 I'm glad you decided to contribute to this project. What are your plans? Anything else you would like to improve in the project?

[phill84]

@mik-laj Thanks for helping get this fix merged! I am usually a couple minors behind the latest release, so this is actually the first bug I found that hasn't been fixed in master. Let's hope that I won't open new PR's too soon or often, at least for time being. 😸