Fix shebang for Python scripts

[jmgrady]

Change the "shebang" for Python scripts from:

#!/usr/bin/env python3

to

#!/usr/bin/env python

The original shebang was set so that Linux users can run the Python scripts by just providing the script name, e.g. ./deploy/scripts/app_release.py --get.

Both of these shebang lines work because the venv module sets up python3 and python to point to the version of Python in the virtual environment. However, when the venv is created on Windows, only the python alias is created. This means that the scripts fail when run from a Git Bash session.

The new shebang works for both environments.

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.59%. Comparing base (6bbfc5b) to head (e646c51).
Report is 14 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3370      +/-   ##
==========================================
- Coverage   74.63%   74.59%   -0.04%     
==========================================
  Files         280      280              
  Lines       10773    10773              
  Branches     1299     1299              
==========================================
- Hits         8040     8036       -4     
- Misses       2367     2370       +3     
- Partials      366      367       +1     

Flag	Coverage Δ
backend	83.81% <ø> (-0.09%)	⬇️
frontend	66.61% <ø> (ø)

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[imnasnainaec]

Reviewed 25 of 25 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @jmgrady)