Fix kwallet again

[samuel-w]

One last try to fixing kwallet. If this doesn't work just remove the kwallet code, its causing more bugs than solutions.

Slightly based it off python-keyring's implementation, https://github.com/jaraco/keyring/blob/main/keyring/backends/kwallet.py#L96.

[samuel-w]

Wait, why don't we just use python-keyring?

[codecov-io]

Codecov Report

Merging #900 (0d6e0ec) into master (84c3d3c) will decrease coverage by 0.01%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##           master     #900      +/-   ##
==========================================
- Coverage   70.32%   70.31%   -0.02%     
==========================================
  Files          56       56              
  Lines        3791     3793       +2     
==========================================
+ Hits         2666     2667       +1     
- Misses       1125     1126       +1     

Impacted Files	Coverage Δ
src/vorta/keyring/kwallet.py	52.50% <16.66%> (-0.14%)	⬇️

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[m3nu]

Doesn't change the functionality of the code, right? Just re-arranges a few things.

[m3nu]

Wait, why don't we just use python-keyring?

We did in the beginning, but there were other issues, like Pyobjc segfaults.

#190 (comment)

[m3nu]

Thanks, cherry-picked a change into #898.