Update to FreeType 2.9.1 (flutter#5991)

Fixes flutter#20303

Author: jason-simmons

DEPS

@@ -350,7 +350,7 @@ deps = {
    Var('chromium_git') + '/external/colorama.git' + '@' + '799604a1041e9b3bc5d2789ecbd7e8db2e18e6b8',
 
   'src/third_party/freetype2':
-   Var('fuchsia_git') + '/third_party/freetype2' + '@' + 'e23a030e9b43c648249477fdf7bf5305d2cc8f59',
+   Var('fuchsia_git') + '/third_party/freetype2' + '@' + '3515a77bb83002b69a2957efdbcb764de4de07da',
 
   'src/third_party/root_certificates':
    Var('dart_git') + '/root_certificates.git' + '@' + Var('dart_root_certificates_rev'),