pyoxidizer: add arch to PyOxidizer MSIs

This is the proper filename pattern. This filename format
wasn't properly implemented when PyOxidizer took over Python 3
MSI generation in 603efb3845ba.

Differential Revision: https://phab.mercurial-scm.org/D11359

rust/hgcli/pyoxidizer.bzl

@@ -255,7 +255,11 b' def make_msi(manifest):'
         path = "defaultrc/editor.rc",
     )
 
-    wix = WiXInstaller("hg", "%s-%s.msi" % (MSI_NAME, VERSION), arch = platform)
+    wix = WiXInstaller(
+        "hg",
+        "%s-%s-%s.msi" % (MSI_NAME, VERSION, platform),
+        arch = platform,
+    )
 
     # Materialize files in the manifest to the install layout.
     wix.add_install_files(manifest)