[AIRFLOW-6625] Explicitly log using utf-8 encoding

[s-mcqueen]

This is the standard encoding supported by Airflow. We should be explicit about logging using
this encoding.

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Issue link: AIRFLOW-6625

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• Description above provides context of the change
• Commit message/PR title starts with [AIRFLOW-NNNN]. AIRFLOW-NNNN = JIRA ID^*
• Unit tests coverage for changes (not needed for documentation changes)
• Commits follow "How to write a good git commit message"
• Relevant documentation is updated including usage instructions.
• I will engage committers as explained in Contribution Workflow Example.

^* For document-only changes commit message can start with [AIRFLOW-XXXX].

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[boring-cyborg]

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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)

Here are some useful points:

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  Adding a new operator? Check this short [guide](https://github
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[codecov-io]

Codecov Report

Merging #7247 into master will decrease coverage by 0.29%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #7247     +/-   ##
=========================================
- Coverage   85.34%   85.05%   -0.3%     
=========================================
  Files         791      791             
  Lines       40135    40137      +2     
=========================================
- Hits        34255    34140    -115     
- Misses       5880     5997    +117

Impacted Files	Coverage Δ
airflow/utils/log/file_task_handler.py	88.76% <100%> (ø)	⬆️
airflow/kubernetes/volume_mount.py	44.44% <0%> (-55.56%)	⬇️
airflow/kubernetes/volume.py	52.94% <0%> (-47.06%)	⬇️
airflow/kubernetes/pod_launcher.py	45.25% <0%> (-46.72%)	⬇️
airflow/kubernetes/refresh_config.py	50.98% <0%> (-23.53%)	⬇️
...viders/cncf/kubernetes/operators/kubernetes_pod.py	76.47% <0%> (-21.18%)	⬇️
airflow/plugins_manager.py	87.57% <0%> (-3.11%)	⬇️
airflow/providers/redis/hooks/redis.py	100% <0%> (ø)	⬆️

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[turbaszek]

Can you please amend the commit message to follow

Commit message/PR title starts with [AIRFLOW-NNNN]. AIRFLOW-NNNN = JIRA ID*

You can use git commit --amend :)

[boring-cyborg]

Awesome work, congrats on your first merged pull request!