test that safe cases do not raise errors

tests/errors/charptr_from_temp.pyx

 # mode: error
 # tag: werror, charptr, conversion, temp
 
+cdef bytes c_s = b"abc"
 s = b"abc"
 
 cdef char* cptr
 
+# constant => ok
+cptr = b"xyz"
+
+# global cdef variable => ok
+cptr = c_s
+
+# pyglobal => warning
 cptr = s
 
+# temp => error
 cptr = s + b"cba"
 
 _ERRORS = """
- 8:8: Obtaining char* from externally modifiable global Python value
-10:9: Obtaining char* from temporary Python value
+16:8: Obtaining char* from externally modifiable global Python value
+19:9: Obtaining char* from temporary Python value
 """