bpo-33029: Fix signatures of getter and setter functions. (GH-10746)

Fix also return type for few other functions (clear, releasebuffer).
diff --git a/Modules/_sre.c b/Modules/_sre.c
index c350979..75f030c 100644
--- a/Modules/_sre.c
+++ b/Modules/_sre.c
@@ -1305,7 +1305,7 @@
 
 /* PatternObject's 'groupindex' method. */
 static PyObject *
-pattern_groupindex(PatternObject *self)
+pattern_groupindex(PatternObject *self, void *Py_UNUSED(ignored))
 {
     if (self->groupindex == NULL)
         return PyDict_New();
@@ -2272,7 +2272,7 @@
     For 0 returns the entire match.");
 
 static PyObject *
-match_lastindex_get(MatchObject *self)
+match_lastindex_get(MatchObject *self, void *Py_UNUSED(ignored))
 {
     if (self->lastindex >= 0)
         return PyLong_FromSsize_t(self->lastindex);
@@ -2280,7 +2280,7 @@
 }
 
 static PyObject *
-match_lastgroup_get(MatchObject *self)
+match_lastgroup_get(MatchObject *self, void *Py_UNUSED(ignored))
 {
     if (self->pattern->indexgroup &&
         self->lastindex >= 0 &&
@@ -2295,7 +2295,7 @@
 }
 
 static PyObject *
-match_regs_get(MatchObject *self)
+match_regs_get(MatchObject *self, void *Py_UNUSED(ignored))
 {
     if (self->regs) {
         Py_INCREF(self->regs);