Make the flight details menu modal.

Prevents players from accidentally deleting flights they're currently
viewing, which would cause an error.

Fixes https://github.com/dcs-liberation/dcs_liberation/issues/2911.

(cherry picked from commit 64e2213f28)

qt_ui/windows/mission/QEditFlightDialog.py

@@ -29,6 +29,7 @@ class QEditFlightDialog(QDialog):
 
         self.setWindowTitle("Edit flight")
         self.setWindowIcon(EVENT_ICONS["strike"])
+        self.setModal(True)
 
         layout = QVBoxLayout()