CI : Set PYTHONHOME on macOS

Without specifically defining `PYTHONHOME`, Python 3.11 reports `Could not find platform dependent libraries <exec_prefix>` and then fails to `import math` etc.

It looks like we're running into a similar issue as the one reported here: python/cpython#95400

Author: murraystevenson

.github/workflows/main/options.posix

@@ -63,4 +63,5 @@ ENV_VARS_TO_IMPORT = "PATH CI"
 
 if platform.system() == "Darwin" :
 	os.environ["DYLD_FRAMEWORK_PATH"] = libs
-	ENV_VARS_TO_IMPORT += " DYLD_FRAMEWORK_PATH"
+	os.environ["PYTHONHOME"] = libs + "/Python.framework/Versions/" + pythonABIVersion
+	ENV_VARS_TO_IMPORT += " DYLD_FRAMEWORK_PATH PYTHONHOME"