patch 8.2.2615: test is sourcing the wrong file

Problem:    Test is sourcing the wrong file.
Solution:   Correct the file name.
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 418435b..956de36 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1575,7 +1575,7 @@
       delcommand CallFunc
       command CallFunc Func()
       def Func()
-        so /tmp/test.vim
+        so XreloadFunc.vim
         g:didTheFunc = 1
       enddef
   END