Fix ftp downloading for older python versions

[mraspaud]

• Closes #xxxx
• Tests added
• Tests passed
• Passes git diff origin/main **/*py | flake8 --diff
• Fully documented

[mraspaud]

@TAlonglong if you want to have a look...

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 38.87%. Comparing base (885f7c2) to head (77cb0f2).
Report is 38 commits behind head on main.

Files with missing lines	Patch %	Lines
trollsched/satpass.py	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
+ Coverage   38.85%   38.87%   +0.02%     
==========================================
  Files          15       15              
  Lines        2082     2086       +4     
==========================================
+ Hits          809      811       +2     
- Misses       1273     1275       +2     

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[TAlonglong]

I don't have any problem with this change

[TAlonglong]

Don't looks like I can merge it.

[adybbroe]

LGTM.
But we should leave python 2 all together shortly!