Mitigate macOS race condition in installer build (GH-6686) (#6689)

(cherry picked from commit fc6aa28bfd)

Co-authored-by: Ned Deily <nad@python.org>

Mac/BuildScript/build-installer.py

@@ -1530,6 +1530,10 @@ def buildDMG():
             shellQuote(os.path.join(WORKDIR, 'installer')),
             shellQuote(imagepath + ".tmp.dmg" )))
 
+    # Try to mitigate race condition in certain versions of macOS, e.g. 10.9,
+    # when hdiutil fails with  "Resource busy"
+
+    time.sleep(10)
 
     if not os.path.exists(os.path.join(WORKDIR, "mnt")):
         os.mkdir(os.path.join(WORKDIR, "mnt"))