Correct a typo in Mainpage.dox

1 job for !153 with patch-1 in 60 minutes (queued for 1 second)
detached
Status Job ID Name Coverage
  Build
failed #62013
linux kf5-qt5 qt5.12

01:00:00

 
Name Stage Failure
failed
linux kf5-qt5 qt5.12 Build The script exceeded the maximum execution time set for the job
Unregistering type class 3
Unregistering type class 6
Unregistering type class 5
Unregistering type class 2

Start 79: test_gdbprinters
Uploading artifacts for failed job
Pulling docker image gitlab/gitlab-runner-helper:x86_64-a998cacd ...
ERROR: Job failed: execution took longer than 1h0m0s seconds