NotificationSubscriber: fix regression introduced by my commit 61ae4984

Instead of resolving all aliases in this hot code path, only add
a special case for text/directory (alias for text/vcard).

Thanks to Konrad Czapla for the investigation of the issue.
2 jobs for !44 with work/dfaure/text_directory in 19 minutes and 40 seconds
detached
Status Job ID Name Coverage
  Build
failed build_clazy_clang_tidy #83898

00:06:42

passed linux kf5-qt5 qt5.15 #83897

00:12:58

1.0%
 
Name Stage Failure
failed
build_clazy_clang_tidy Build
[ 19%] 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