tests/cpydiff: Fix markup where "`" (xref) was used instead of "``" (code).

tests/cpydiff/builtin_next_arg2.py

@@ -2,7 +2,7 @@
 categories: Modules,builtins
 description: Second argument to next() is not implemented
 cause: MicroPython is optimised for code space.
-workaround: Instead of `val = next(it, deflt)` use::
+workaround: Instead of ``val = next(it, deflt)`` use::
 
     try:
         val = next(it)

tests/cpydiff/types_str_ljust_rjust.py

@@ -2,6 +2,6 @@
 categories: Types,str
 description: str.ljust() and str.rjust() not implemented
 cause: MicroPython is highly optimized for memory usage. Easy workarounds available.
-workaround: Instead of `s.ljust(10)` use `"%-10s" % s`, instead of `s.rjust(10)` use `"% 10s" % s`. Alternatively, `"{:<10}".format(s)` or `"{:>10}".format(s)`.
+workaround: Instead of ``s.ljust(10)`` use ``"%-10s" % s``, instead of ``s.rjust(10)`` use ``"% 10s" % s``. Alternatively, ``"{:<10}".format(s)`` or ``"{:>10}".format(s)``.
 """
 print('abc'.ljust(10))