Read the global color scheme name from its file

Adds the same fix as in kde/kate!46. KColorSchemeManager operates on the user
visible Scheme names. They can generally differ from the names of the *.colors
files which are saved in kdeglobals. To correctly select the global active scheme
we have to read the name from the file.
1 job for !91 with colorschememanager in 60 minutes (queued for 3 minutes and 54 seconds)
Status Job ID Name Coverage
failed #30138
linux kf5-qt5 qt5.12


Name Stage Failure
linux kf5-qt5 qt5.12 Build The script exceeded the maximum execution time set for the job
        Start  86: test_qmljsdeclarations
kf5.kinit.klauncher: new app ":1.49"
kf5.kinit.klauncher: new app "org.kdevelop.kdevplatform-lock-e7f7e82d-d8e2-4afa-a52b-23edc9707c1e"
86/123 Test #86: test_qmljsdeclarations .................. Passed 5.82 sec
Start 87: test_files
kf5.kinit.klauncher: new app ":1.50"
kf5.kinit.klauncher: new app "org.kdevelop.kdevplatform-lock-28b5d259-1713-41aa-9199-3c142cf20593"
Pulling docker image gitlab/gitlab-runner-helper:x86_64-ac8e767a ...
ERROR: Job failed: execution took longer than 1h0m0s seconds