gpython: tests: Prepare expected repr properly

In several places we were preparing repr of a string as '%s' which works
ok most of the time but leads to failure if string contains '\'
characters e.g. if it represents a path and we are running on windows:

        def test_pymain():
            from golang import b

            ....

            # -m <module>
            _ = pyout(['-m', 'hello', 'abc', 'def'], cwd=testdata)
            # realpath rewrites e.g. `local/lib -> lib` if local/lib is symlink
            hellopy = realpath(join(testdata, 'hello.py'))
    >       assert _ == b"hello\nworld\n['%s', 'abc', 'def']\n" % b(hellopy)
    E       assert b"hello\nworld\n['Z:\\\\home\\\\kirr\\\\src\\\\tools\\\\go\\\\pygo-win\\\\pygolang\\\\gpython\\\\testdata\\\\hello.py', 'abc', 'def'
    ]\n" == b"hello\nworld\n['Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\pygolang\\gpython\\testdata\\hello.py', 'abc', 'def']\n"
    E         At index 17 diff: b'\\' != b'h'
    E         Full diff:
    E           (
    E         -  b"hello\nworld\n['Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\pygolang\\gpytho"
    E         ?                                                                  ------------
    E         +  b"hello\nworld\n['Z:\\\\home\\\\kirr\\\\src\\\\tools\\\\go\\\\pygo-win\\\\pygo"
    E         ?                        ++    ++        ++   ++         ++  ++            ++
    E         -  b"n\\testdata\\hello.py', 'abc', 'def']\n",
    E         +  b"lang\\\\gpython\\\\testdata\\\\hello.py', 'abc', 'def']\n",
    E         ?    ++ ++++++++++++++            ++
    E           )

    gpython\gpython_test.py:183: AssertionError

-> Fix it by preparing repr via repr(...) properly.

gpython/gpython_test.py

 # -*- coding: utf-8 -*-
-# Copyright (C) 2019-2021  Nexedi SA and Contributors.
+# Copyright (C) 2019-2023  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -180,7 +180,7 @@ def test_pymain():
     _ = pyout(['-m', 'hello', 'abc', 'def'], cwd=testdata)
     # realpath rewrites e.g. `local/lib -> lib` if local/lib is symlink
     hellopy = realpath(join(testdata, 'hello.py'))
-    assert _ == b"hello\nworld\n['%s', 'abc', 'def']\n" % b(hellopy)
+    assert _ == b"hello\nworld\n[%s, 'abc', 'def']\n" % b(repr(hellopy))
     # -m<module>
     __ = pyout(['-mhello', 'abc', 'def'], cwd=testdata)
     assert __ == _
@@ -191,8 +191,8 @@ def test_pymain():
 
     # -i after stdin (also tests interactive mode as -i forces interactive even on non-tty)
     d = {
-        b'hellopy': b(hellopy),
-        b'ps1':     b'' # cpython emits prompt to stderr
+        b'repr(hellopy)': b(repr(hellopy)),
+        b'ps1':           b'' # cpython emits prompt to stderr
     }
     if is_pypy and not is_gpython:
         d[b'ps1'] = b'>>>> ' # native pypy emits prompt to stdout and >>>> instead of >>>
@@ -208,7 +208,7 @@ def test_pymain():
     assert _ == b"hello\nworld\n['-c']\n%(ps1)s'~~HELLO~~'\n%(ps1)s"    % d
     # -i after -m
     _ = pyout(['-i', '-m', 'hello'], stdin=b'world.tag', cwd=testdata)
-    assert _ == b"hello\nworld\n['%(hellopy)s']\n%(ps1)s'~~WORLD~~'\n%(ps1)s"  % d
+    assert _ == b"hello\nworld\n[%(repr(hellopy))s]\n%(ps1)s'~~WORLD~~'\n%(ps1)s"  % d
     # -i after file
     _ = pyout(['-i', 'testdata/hello.py'], stdin=b'tag', cwd=here)
     assert _ == b"hello\nworld\n['testdata/hello.py']\n%(ps1)s'~~HELLO~~'\n%(ps1)s" % d