Use json dump without inserting newlines when saving to keyring on linux

[JBiene]

Hi all,

i feel like inserting newlines in the json string in #756 introduced problems.

I was trying to set up Ente Auth (https://github.com/ente-io/ente) which made the Default_keyring unusable in all apps that use the same keyring on each reboot. This issue was also mentioned here #951 and here ente-io/ente#4769.

System:
Linux 6.17.7-arch1-2
libsecret 0.21.7-1
gnome-keyring 48.0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.37%. Comparing base (87dca4c) to head (3ec6d52).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1001   +/-   ##
========================================
  Coverage    99.37%   99.37%           
========================================
  Files            9        9           
  Lines          161      161           
========================================
  Hits           160      160           
  Misses           1        1           

Flag	Coverage Δ
unittests	99.37% <ø> (ø)

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