bpo-41094: Fix decoding errors with audit when open files. (GH-21095)

(cherry picked from commit 6c6810d98979add7a89391c3c38990d0859f7a29)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index b7b7058..e4fed51 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -1353,7 +1353,7 @@
                                       returncode=1)
 
     def test_audit_run_interactivehook(self):
-        startup = os.path.join(self.oldcwd, support.TESTFN) + ".py"
+        startup = os.path.join(self.oldcwd, support.TESTFN) + (support.TESTFN or '') + ".py"
         with open(startup, "w", encoding="utf-8") as f:
             print("import sys", file=f)
             print("sys.__interactivehook__ = lambda: None", file=f)
@@ -1366,7 +1366,7 @@
             os.unlink(startup)
 
     def test_audit_run_startup(self):
-        startup = os.path.join(self.oldcwd, support.TESTFN) + ".py"
+        startup = os.path.join(self.oldcwd, support.TESTFN) + (support.TESTFN or '') + ".py"
         with open(startup, "w", encoding="utf-8") as f:
             print("pass", file=f)
         try: