pin meson==0.55.3 to try fix PermissionError on windows

with latest meson 0.56, Appveyor CI sometimes fails with

https://ci.appveyor.com/project/googlefonts/ots-python/builds/36989591/job/6e2orcxjbfyy6j3b#L184

sometimes it passes.. I have no idea.

Author: anthrotype

tox.ini

@@ -28,7 +28,7 @@ deps =
     pip
     setuptools
     wheel
-    git+https://github.com/mesonbuild/meson.git#egg=meson
+    meson==0.55.3
     ninja
 skip_install = true
 commands =