ci: hard-code meson 1.7.2

1.8 broke default subproject warning_level

Author: cfillion

.appveyor.yml

@@ -4,8 +4,8 @@ stack: python 3
 
 install:
   - sh:  sudo -H "$(command -v python3)" -m ensurepip --upgrade
-  - sh:  sudo -H "$(command -v pip3)" install meson
-  - cmd: pip3 install meson
+  - sh:  sudo -H "$(command -v pip3)" install meson==1.7.2
+  - cmd: pip3 install meson==1.7.2
   - git submodule update --init --depth 1
 build_script:
   - sh:  meson setup build --buildtype=release ${meson_options[@]}