[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/.circleci/config.yml b/.circleci/config.yml
index 0c857ba..84f59bb 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -68,7 +68,7 @@
     steps:
       - checkout
       - run: apk update && apk add ragel gcc g++ glib-dev freetype-dev cairo-dev git py3-pip ninja
-      - run: pip3 install meson==0.47.0
+      - run: pip3 install meson==0.52.0
       - run: meson build --buildtype=minsize
       - run: ninja -Cbuild -j9
       - run: meson test -Cbuild --print-errorlogs
diff --git a/.github/workflows/linux-ci.yml b/.github/workflows/linux-ci.yml
index 407d214..5a82f7d 100644
--- a/.github/workflows/linux-ci.yml
+++ b/.github/workflows/linux-ci.yml
@@ -14,7 +14,7 @@
     - uses: actions/checkout@v2
     - name: install dependencies
       run: sudo apt-get install pkg-config gcc ragel gcovr gtk-doc-tools libfreetype6-dev libglib2.0-dev libcairo2-dev libicu-dev libgraphite2-dev python3 python3-setuptools ninja-build gobject-introspection libgirepository1.0-dev
-    - run: sudo pip3 install fonttools meson==0.47.0
+    - run: sudo pip3 install fonttools meson==0.52.0
     - name: run
       run: meson build -Db_coverage=true --auto-features=enabled -Dgraphite=enabled -Dchafa=disabled -Doptimization=2
     - name: ci
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
diff --git a/src/meson.build b/src/meson.build
index cbe57e9..07c477c 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -290,7 +290,7 @@
   'hb-gobject-structs.h',
 )
 
-ragel = find_program('ragel', required: false)
+ragel = find_program('ragel', version: '6.10', required: false)
 if not ragel.found()
   warning('You have to install ragel if you are going to develop HarfBuzz itself')
 else