Make correct use of Qt signal 'emit' keyword

[claucambra]

Fixes several instances of bad/incorrect/missing use of emit

[codecov]

Codecov Report

Merging #5287 (30db3f3) into master (7f6b18b) will decrease coverage by 0.09%.
The diff coverage is 16.66%.

❗ Current head 30db3f3 differs from pull request most recent head 377b4f6. Consider uploading reports for the commit 377b4f6 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5287      +/-   ##
==========================================
- Coverage   57.59%   57.50%   -0.10%     
==========================================
  Files         139      139              
  Lines       17596    17596              
==========================================
- Hits        10135    10119      -16     
- Misses       7461     7477      +16     

Impacted Files	Coverage Δ
src/libsync/creds/dummycredentials.cpp	0.00% <0.00%> (ø)
src/libsync/creds/httpcredentials.cpp	6.91% <0.00%> (ø)
src/libsync/discoveryphase.cpp	73.53% <0.00%> (ø)
src/libsync/discovery.cpp	85.93% <50.00%> (ø)
src/libsync/vfs/cfapi/hydrationjob.cpp	52.38% <0.00%> (-3.71%)	⬇️
src/libsync/vfs/cfapi/vfs_cfapi.cpp	83.07% <0.00%> (-2.37%)	⬇️
src/libsync/vfs/cfapi/cfapiwrapper.cpp	72.50% <0.00%> (-1.82%)	⬇️
src/libsync/syncengine.cpp	81.32% <0.00%> (-0.44%)	⬇️
src/libsync/propagatedownload.cpp	64.90% <0.00%> (+1.17%)	⬆️

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

30.8% Coverage
0.0% Duplication

[nextcloud-desktop-bot]

AppImage file: nextcloud-PR-5287-377b4f6ddfef4f21822287f3c04cb64fc8013c11-x86_64.AppImage

To test this change/fix you can simply download above AppImage file and test it.

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