test: py: test_shell_run() with CONFIG_HUSH_PARSER=n

The hush parser not enabled for some boards, e.g.
sipeed_maix_bitm_defconfig.

With CONFIG_HUSH_PARSER=n a double quotation mark is not interpreted as the
beginning of a string. Use a single quotation mark instead.

Furthermore without the hush parser variables have to be referenced as
${varname}. Add the missing braces.

Reported-by: Sean Anderson <seanga2@gmail.com>
Fixes: 8b86c609b860 ("test/py: add test of basic shell functionality")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/test/py/tests/test_shell_basics.py b/test/py/tests/test_shell_basics.py
index f54f7b7..68a3f89 100644
--- a/test/py/tests/test_shell_basics.py
+++ b/test/py/tests/test_shell_basics.py
@@ -34,11 +34,11 @@
 def test_shell_run(u_boot_console):
     """Test the "run" shell command."""
 
-    u_boot_console.run_command('setenv foo "setenv monty 1; setenv python 2"')
+    u_boot_console.run_command('setenv foo \'setenv monty 1; setenv python 2\'')
     u_boot_console.run_command('run foo')
-    response = u_boot_console.run_command('echo $monty')
+    response = u_boot_console.run_command('echo ${monty}')
     assert response.strip() == '1'
-    response = u_boot_console.run_command('echo $python')
+    response = u_boot_console.run_command('echo ${python}')
     assert response.strip() == '2'
     u_boot_console.run_command('setenv foo')
     u_boot_console.run_command('setenv monty')