golang_str: tests: Adjust test_strings_index2 not to depend on repr(ustr|bstr)

repr(ustr|bstr) will change behaviour depending on whether we are
running under regular python, or gpython with string types replaced by
bstr/ustr. But this test is completely orthogonal to that. -> Let's
untie it from particular repr behaviour by emitting verified items in
quoted form + asserting their types in the code.

golang/testprog/golang_test_str_index2.py

 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
-# Copyright (C) 2022  Nexedi SA and Contributors.
+# Copyright (C) 2022-2023  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -29,7 +29,8 @@ from builtin str/unicode, does not get into our way.
 
 from __future__ import print_function, absolute_import
 
-from golang import b, u
+from golang import b, u, bstr, ustr
+from golang.gcompat import qq
 
 
 def main():
@@ -37,8 +38,10 @@ def main():
     bs = b("миру мир")
 
     def emit(what, uobj, bobj):
-        print("u"+what, repr(uobj))
-        print("b"+what, repr(bobj))
+        assert type(uobj) is ustr
+        assert type(bobj) is bstr
+        print("u"+what, qq(uobj))
+        print("b"+what, qq(bobj))
 
     emit("s",       us,        bs)
     emit("s[:]",    us[:],     bs[:])

golang/testprog/golang_test_str_index2.txt

-us u('миру мир')
-bs b('миру мир')
-us[:] u('миру мир')
-bs[:] b('миру мир')
-us[0:1] u('м')
-bs[0:1] b(b'\xd0')
-us[0:2] u('ми')
-bs[0:2] b('м')
-us[1:2] u('и')
-bs[1:2] b(b'\xbc')
-us[0:-1] u('миру ми')
-bs[0:-1] b(b'миру ми\xd1')
+us "миру мир"
+bs "миру мир"
+us[:] "миру мир"
+bs[:] "миру мир"
+us[0:1] "м"
+bs[0:1] "\xd0"
+us[0:2] "ми"
+bs[0:2] "м"
+us[1:2] "и"
+bs[1:2] "\xbc"
+us[0:-1] "миру ми"
+bs[0:-1] "миру ми\xd1"