buildMozilaMach: use latest icu from 115.0

The beta and devedition browsers already require icu73, so we need to
relax this pin again.

firefox-beta-unwrapped> 0:24.92 ERROR: Requested 'icu-i18n >= 73.1' but version of icu-i18n is 72.1

pkgs/applications/networking/browsers/firefox/common.nix

@@ -54,6 +54,7 @@
 , glib
 , gnum4
 , gtk3
+, icu
 , icu72
 , libGL
 , libGLU
@@ -440,9 +441,6 @@ buildStdenv.mkDerivation ({
     freetype
     glib
     gtk3
-    # icu73 changed how it follows symlinks which breaks in the firefox sandbox
-    # https://bugzilla.mozilla.org/show_bug.cgi?id=1839287
-    icu72
     libffi
     libGL
     libGLU
@@ -470,6 +468,9 @@ buildStdenv.mkDerivation ({
     zip
     zlib
   ]
+  # icu73 changed how it follows symlinks which breaks in the firefox sandbox
+  # https://bugzilla.mozilla.org/show_bug.cgi?id=1839287
+  ++ [ (if (lib.versionAtLeast version "115") then icu else icu72) ]
   ++ [ (if (lib.versionAtLeast version "103") then nss_latest else nss_esr) ]
   ++ lib.optional  alsaSupport alsa-lib
   ++ lib.optional  jackSupport libjack2