[libnotify] build: Do not require g-ir-scanner on introspection=auto

[Marco Trevisan <marcotrevi src gnome org>]

commit d348a36a053bee9d45fdd3f90b0d0682e0ffdf25
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Thu Apr 21 16:54:49 2022 +0200

    build: Do not require g-ir-scanner on introspection=auto

 libnotify/meson.build | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/libnotify/meson.build b/libnotify/meson.build
index c1fb485..2258a1d 100644
--- a/libnotify/meson.build
+++ b/libnotify/meson.build
@@ -69,8 +69,9 @@ pkgconfig.generate(libnotify_lib,
 )
 
 introspection = get_option('introspection')
-if not introspection.disabled()
-  find_program('g-ir-scanner', required: introspection.enabled())
+g_ir_scanner = find_program('g-ir-scanner', required: introspection.enabled())
+
+if g_ir_scanner.found() and not introspection.disabled()
   gnome.generate_gir(libnotify_lib,
     sources: headers + sources + enum_types,
     namespace: 'Notify',