Addon Manager: use versioned Python package dirs

src/App/FreeCADInit.py

@@ -171,7 +171,15 @@ def InitApplications():
     sys.path = [ModDir] + libpaths + [ExtDir] + sys.path
 
     # The AddonManager may install additional Python packages in
-    # this path:
+    # these paths:
+    import platform
+    major,minor,_ = platform.python_version_tuple()
+    vendor_path = os.path.join(
+        FreeCAD.getUserAppDataDir(), "AdditionalPythonPackages",f"py{major}{minor}"
+    )
+    if os.path.isdir(vendor_path):
+        sys.path.append(vendor_path)
+
     additional_packages_path = os.path.join(FreeCAD.getUserAppDataDir(),"AdditionalPythonPackages")
     if os.path.isdir(additional_packages_path):
         sys.path.append(additional_packages_path)