build: bump version to 1.12.4

- query when quitting emacs with unhandled marks in a headers buffer
- fix mime-handling
- update sent handling (simplifying it)
- some internal improvements
- number of small fixes / updates
- documentation updates
- re-enable a specific database lock; this makes indexing a bit slower,
  but hopefully avoids some db corruption.

meson.build

@@ -17,7 +17,7 @@
 ################################################################################
 # project setup
 project('mu', ['c', 'cpp'],
-        version: '1.12.3',
+        version: '1.12.4',
         meson_version: '>= 0.56.0',
         license: 'GPL-3.0-or-later',
         default_options : [
@@ -28,7 +28,7 @@ project('mu', ['c', 'cpp'],
 
 # hard-code the date here (for reproduciblity); we derive the dates used in e.g.
 # documentation from this.
-mu_date='2024-04-08'
+mu_date='2024-04-15'
 
 # installation paths
 prefixdir = get_option('prefix')