Changing X509at_get0_data_by_OBJ to expect const stack of X509_ATTRIBUTE

CLA: trivial
Reviewed-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13062)

crypto/x509/x509_att.c

@@ -149,7 +149,7 @@ STACK_OF(X509_ATTRIBUTE) *X509at_add1_attr_by_txt(STACK_OF(X509_ATTRIBUTE)
     return ret;
 }
 
-void *X509at_get0_data_by_OBJ(STACK_OF(X509_ATTRIBUTE) *x,
+void *X509at_get0_data_by_OBJ(const STACK_OF(X509_ATTRIBUTE) *x,
                               const ASN1_OBJECT *obj, int lastpos, int type)
 {
     int i;

include/openssl/x509.h.in

@@ -975,7 +975,7 @@ STACK_OF(X509_ATTRIBUTE) *X509at_add1_attr_by_txt(STACK_OF(X509_ATTRIBUTE)
                                                   int type,
                                                   const unsigned char *bytes,
                                                   int len);
-void *X509at_get0_data_by_OBJ(STACK_OF(X509_ATTRIBUTE) *x,
+void *X509at_get0_data_by_OBJ(const STACK_OF(X509_ATTRIBUTE) *x,
                               const ASN1_OBJECT *obj, int lastpos, int type);
 X509_ATTRIBUTE *X509_ATTRIBUTE_create_by_NID(X509_ATTRIBUTE **attr, int nid,
                                              int atrtype, const void *data,