Make sure only one sync job is running at a time

[JonasMayerDev]

Before running sync worker, check if another sync worker is already running. Before in theory 2 sync jobs could run and potentially mess with each other (maybe leads to https://github.com/nextcloud/android/issues/11974)

• [X] Tests written, or not not needed

[JonasMayerDev]

Problem: With current implementation when periodic sync worker is started and immediate filesync is already running because of changed files it will skip periodic sync which is not intended... But it is really unlikely since immediate file sync with changed files should only run for under 1 sec.

[github-actions[bot]]

Codacy

Lint

Type	master	PR
Warnings	72	72
Errors	3	3

SpotBugs

Category	Base	New
Bad practice	66	66
Correctness	73	73
Dodgy code	349	349
Experimental	1	1
Internationalization	7	7
Malicious code vulnerability	2	2
Multithreaded correctness	6	6
Performance	57	57
Security	19	19
Total	580	580

[github-actions[bot]]

APK file: https://www.kaminsky.me/nc-dev/android-artifacts/12372.apk



To test this change/fix you can simply download above APK file and install and test it in parallel to your existing Nextcloud app.