python3Packages.meson-python: fixup darwin build again

The patch doesn't fully fix the problem:
mesonbuild/meson-python#761 (comment)
and I want to avoid rebuilding on Linux again this iteration.

Author: vcunat

pkgs/development/python-modules/meson-python/default.nix

@@ -1,5 +1,6 @@
 {
   lib,
+  stdenv,
   buildPythonPackage,
   fetchPypi,
   fetchpatch,
@@ -56,6 +57,18 @@ buildPythonPackage rec {
     pytest-mock
   ];
 
+  # meson-python respectes MACOSX_DEPLOYMENT_TARGET, but compares it with the
+  # actual platform version during tests, which mismatches.
+  # https://github.com/mesonbuild/meson-python/issues/760
+  # FIXME: drop in 0.19.0
+  preCheck =
+    if stdenv.hostPlatform.isDarwin then
+      ''
+        unset MACOSX_DEPLOYMENT_TARGET
+      ''
+    else
+      null;
+
   setupHooks = [ ./add-build-flags.sh ];
 
   meta = {