Remove const qualifier from function declaration.

due to complier complians

/home/reshke/cloudberry/contrib/pax_storage/../../src/include/utils/numeric.h:319:8: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
  319 | extern const bool init_var_from_str(const char *str, const char *cp, NumericVar *dest, const char **endptr,
      |        ^~~~~

Author: reshke

src/backend/utils/adt/numeric.c

@@ -7059,7 +7059,7 @@ zero_numeric_var(NumericVar *var)
  * Returns true on success, false on failure (if escontext points to an
  * ErrorSaveContext; otherwise errors are thrown).
  */
-const bool
+bool
 init_var_from_str(const char *str, const char *cp, NumericVar *dest, const char **endptr,
 				  Node *escontext)
 {