prefs: fix memory leak

[rbuj]

Direct leak of 424 byte(s) in 1 object(s) allocated from:
    #0 0x7fd3bc5ee93f in __interceptor_malloc (/lib64/libasan.so.6+0xae93f)
    #1 0x7fd3bb342b7f in g_malloc ../glib/gmem.c:106
    #2 0x7fd3bb342ec2 in g_malloc_n ../glib/gmem.c:344
    #3 0x7fd3bb642c1b in g_settings_schema_list_keys ../gio/gsettingsschema.c:1112
    #4 0x7fd3bc40e5e7 in init_bindings core/prefs.c:1753
    #5 0x7fd3bc40e73b in init_window_bindings core/prefs.c:1774
    #6 0x7fd3bc40ba95 in meta_prefs_init core/prefs.c:978
    #7 0x4040fb in main core/main.c:467
    #8 0x7fd3bae40b74 in __libc_start_main (/lib64/libc.so.6+0x27b74)

Direct leak of 523 byte(s) in 51 object(s) allocated from:
    #0 0x7f208ab9893f in __interceptor_malloc (/lib64/libasan.so.6+0xae93f)
    #1 0x7f20898ecb7f in g_malloc ../glib/gmem.c:106
    #2 0x7f20898ecec2 in g_malloc_n ../glib/gmem.c:344
    #3 0x7f208990f1a5 in g_strdup ../glib/gstrfuncs.c:364
    #4 0x7f208993c9b4 in g_variant_dup_string ../glib/gvariant.c:1537
    #5 0x7f2089bf3d0d in g_settings_get_string ../gio/gsettings.c:1809
    #6 0x7f208a9b8651 in init_bindings core/prefs.c:1758
    #7 0x7f208a9b8738 in init_window_bindings core/prefs.c:1775
    #8 0x7f208a9b5a95 in meta_prefs_init core/prefs.c:978
    #9 0x4040fb in main core/main.c:467
    #10 0x7f20893eab74 in __libc_start_main (/lib64/libc.so.6+0x27b74)

[raveit65]

@rbuj Can you please push PR to get a deployment?

[rbuj]

done

[raveit65]

Hmm, during testing keybindings with this PR i noticed that i can choose the same keybinding for 2 keys, without a warning. But this isn't related to this PR as it happens with marco-1.26 too. .....sigh.