CI: update AppImage configs

- Use GiB terminology like the example configs already do,
   to match commit 599b34c7

data/config-appimage/modules/welcome.conf

@@ -15,12 +15,12 @@ showReleaseNotesUrl:    true
 # that are checked. They may not match with the actual requirements
 # imposed by other modules in the system.
 requirements:
-    # Amount of available disk, in GB. Floating-point is allowed here.
+    # Amount of available disk, in GiB. Floating-point is allowed here.
     # Note that this does not account for *usable* disk, so it is possible
     # to pass this requirement, yet have no space to install to.
     requiredStorage:    5.5
 
-    # Amount of available RAM, in GB. Floating-point is allowed here.
+    # Amount of available RAM, in GiB. Floating-point is allowed here.
     requiredRam:        1.0
 
     # To check for internet connectivity, Calamares does a HTTP GET