patch 8.2.2187: Python 3 test fails sometimes

Problem:    Python 3 test fails sometimes. (Christian Brabandt)
Solution:   Accept two SystemError messages.
diff --git a/src/testdir/test_python3.vim b/src/testdir/test_python3.vim
index 1a86a7e..7765071 100644
--- a/src/testdir/test_python3.vim
+++ b/src/testdir/test_python3.vim
@@ -12,6 +12,7 @@
   return {'a': 1}
 endfunction
 
+let s:system_error_pat = 'Vim(py3):SystemError: \(<built-in function eval> returned NULL without setting an error\|error return without exception set\)'
 
 " This function should be called first. This sets up python functions used by
 " the other tests.
@@ -539,11 +540,11 @@
 func Test_python3_list()
   " Try to convert a null List
   call AssertException(["py3 t = vim.eval('test_null_list()')"],
-        \ 'Vim(py3):SystemError: <built-in function eval> returned NULL without setting an error')
+        \ s:system_error_pat)
 
   " Try to convert a List with a null List item
   call AssertException(["py3 t = vim.eval('[test_null_list()]')"],
-        \ 'Vim(py3):SystemError: <built-in function eval> returned NULL without setting an error')
+        \ s:system_error_pat)
 
   " Try to bind a null List variable (works because an empty list is used)
   let cmds =<< trim END
@@ -582,11 +583,11 @@
 func Test_python3_dict()
   " Try to convert a null Dict
   call AssertException(["py3 t = vim.eval('test_null_dict()')"],
-        \ 'Vim(py3):SystemError: <built-in function eval> returned NULL without setting an error')
+        \ s:system_error_pat)
 
   " Try to convert a Dict with a null List value
   call AssertException(["py3 t = vim.eval(\"{'a' : test_null_list()}\")"],
-        \ 'Vim(py3):SystemError: <built-in function eval> returned NULL without setting an error')
+        \ s:system_error_pat)
 
   " Try to convert a Dict with a null string key
   py3 t = vim.eval("{test_null_string() : 10}")
@@ -1119,7 +1120,7 @@
   let l = [test_null_list()]
   py3 ll = vim.bindeval('l')
   call AssertException(["py3 x = ll[:]"],
-        \ "Vim(py3):SystemError: error return without exception set")
+        \ s:system_error_pat)
 endfunc
 
 " Vars