[meson] Require ragel 6.10

Ragel 7 is also not stable from upstream's point of view.

This uses “version” argument find_program(), which was introduced in
meson 0.52.0, so I raised the minimum required meson version
accordingly.
diff --git a/meson.build b/meson.build
index a552a60..5b4849a 100644
--- a/meson.build
+++ b/meson.build
@@ -1,5 +1,5 @@
 project('harfbuzz', 'c', 'cpp',
-  meson_version: '>= 0.47.0',
+  meson_version: '>= 0.52.0',
   version: '2.9.1',
   default_options: [
     'cpp_eh=none',          # Just to support msvc, we are passing -fno-rtti also anyway