Dump dockerfile base image to python 3.10

[bvolkmer]

See #275

[bvolkmer]

I tested it on my personal instance, which works with eBay Kleinanzeigen and wg-gesucht.de. Immoscout24 test is not possible in docker due to #272.

[codders]

Looks good - thank you!

[codecov]

Codecov Report

Merging #280 (56e9073) into main (4b20fe2) will decrease coverage by 0.16%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #280      +/-   ##
==========================================
- Coverage   64.42%   64.26%   -0.16%     
==========================================
  Files          36       36              
  Lines        1875     1875              
  Branches      251      251              
==========================================
- Hits         1208     1205       -3     
- Misses        603      604       +1     
- Partials       64       66       +2     

Impacted Files	Coverage Δ
flathunter/crawl_immowelt.py	67.69% <0.00%> (-3.08%)	⬇️
flathunter/abstract_crawler.py	38.46% <0.00%> (-1.40%)	⬇️
flathunter/crawl_immobiliare.py	94.87% <0.00%> (+2.56%)	⬆️

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