device-nokia-n900: fix Fn key in latest xkb-config (MR 3596)

Explicitly set Fn key as Mod5. In xkeyboard-config up to 2.36, this was somehow
set implicitly, since it was working, although I am not sure where/how. In 2.37
it only works when specified.

[ci:skip-build]: already built successfully in CI

device/community/device-nokia-n900/APKBUILD

@@ -3,7 +3,7 @@
 # Co-Maintainer: Danct12 <danct12@disroot.org>
 pkgname=device-nokia-n900
 pkgver=8.3
-pkgrel=1
+pkgrel=2
 pkgdesc="Nokia N900"
 url="https://postmarketos.org"
 arch="armv7"
@@ -192,6 +192,6 @@ b50e7f37ffb1fa0bb782b117a4e8bcfdb722b6127c3e5d643e90cd901a1f4e65e77a0773ed418673
 3ae550b50f963695be30eb0e03c31fe7a92aad73174873efe5b73d446b74da5763b6fe9495b91bbdbe307723f6510ebc6639437904815e9251a094ce9bec5b11  uboot-script.cmd
 9e72035c88632d12895534e5aa5746f2c130c7dcdafa8702748d62b71ed0e1b5911b6e1f07f9b9e39b6072bbb662f66aead585baa1dcacb7d8c8953ca89b6762  10-nokia-modem.rules
 c6012aef28b096141b924fced226ec99fb93eb53b69c064a8887d8fecdf8dc08a3ba3db399e18d88374c6ef4c59013a30699c7e4d76e5cb771040582573a0527  90-touchscreen-dev.rules
-654f2e1b8b7b64fc8c82a5f3c2b76b9d88f56d8dda520c1ce162648d65031bf62702e3bd43e135ab040b927c403f9970d6efae53f957bf1e55954125b358b313  x11-keymap
+737d9e57e219a0220c5b1943375f325309323344fdf06973546c7d88ed9aec857657abd6b7861669873574f865e1c99719d411e0564dbfebe028f9e77d308491  x11-keymap
 a91f98daa60efa2beb2ff6b405097f92edca5f1bbb9e7675499139be52ca2570712f8f06f9032ef29f636f99c8f8da8b992f746eab6424aac04260c16158bcc2  xorg.conf
 "

device/community/device-nokia-n900/x11-keymap

@@ -484,6 +484,7 @@ xkb_symbols "modifiers" {
 
     // Fn key (right alt) switches to 3rd level
     include "level3(ralt_switch)"
+    modifier_map Mod5 { ISO_Level3_Shift };
 };
 
 partial hidden alphanumeric_keys