gh-126072: do not add None to co_consts if there is no docstring (GH-126101)

Include/cpython/code.h

@@ -174,6 +174,11 @@ struct PyCodeObject _PyCode_DEF(1);
 
 #define CO_NO_MONITORING_EVENTS 0x2000000
 
+/* Whether the code object has a docstring,
+   If so, it will be the first item in co_consts
+*/
+#define CO_HAS_DOCSTRING 0x4000000
+
 /* This should be defined if a future statement modifies the syntax.
    For example, when a keyword is added.
 */

Include/internal/pycore_symtable.h

@@ -123,6 +123,7 @@ typedef struct _symtable_entry {
     unsigned ste_comp_iter_target : 1; /* true if visiting comprehension target */
     unsigned ste_can_see_class_scope : 1; /* true if this block can see names bound in an
                                              enclosing class scope */
+    unsigned ste_has_docstring : 1; /* true if docstring present */
     int ste_comp_iter_expr; /* non-zero if visiting a comprehension range expression */
     _Py_SourceLocation ste_loc; /* source location of block */
     struct _symtable_entry *ste_annotation_block; /* symbol table entry for this entry's annotations */