Revert "GH-128914: Remove conditional stack effects from bytecodes.c and the code generators (GH-128918)" (GH-129202)

The commit introduced a ~2.5-3% regression in the free threading build.

This reverts commit ab61d3f430.

Python/flowgraph.c

@@ -1836,6 +1836,12 @@ optimize_basic_block(PyObject *const_cache, basicblock *bb, PyObject *consts)
                     INSTR_SET_OP0(inst, NOP);
                 }
                 break;
+            case LOAD_GLOBAL:
+                if (nextop == PUSH_NULL && (oparg & 1) == 0) {
+                    INSTR_SET_OP1(inst, LOAD_GLOBAL, oparg | 1);
+                    INSTR_SET_OP0(&bb->b_instr[i + 1], NOP);
+                }
+                break;
             case COMPARE_OP:
                 if (nextop == TO_BOOL) {
                     INSTR_SET_OP0(inst, NOP);