entitytreemodel: Add more debug output

Helps finding the offending collection at least.
2 jobs for !43 with feature/add-debug-output in 19 minutes and 39 seconds (queued for 81 minutes and 45 seconds)
detached
Status Job ID Name Coverage
  Build
failed #82853
build_clazy_clang_tidy

00:06:50

passed #82852
linux kf5-qt5 qt5.15

00:12:48

1.0%
 
Name Stage Failure
failed
build_clazy_clang_tidy Build
[ 21%] Built target akonadi_control
make[1]: *** [CMakeFiles/Makefile2:2683: src/core/CMakeFiles/KF5AkonadiCore.dir/all] Error 2
make: *** [Makefile:160: all] Error 2
Uploading artifacts for failed job
Uploading artifacts...
WARNING: build/clang-tidy-report.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit code 1