Fix #1893: git commit should be able to wait for Kate editor

[andrei-korshikov]

Kate editor must be started with "--block" option so git commit can patiently wait for the editor to close the commit message file.

• [x] I provide my work under the project license.
• [x] I grant such license of my work as is required for the purposes of future print editions to Ben Straub and Scott Chacon.

Context

Fixes #1893

[ben]

Thanks! ✨