bpo-32088: Display Deprecation in debug mode (#4474)

When Python is build is debug mode (Py_DEBUG), DeprecationWarning,
PendingDeprecationWarning and ImportWarning warnings are now
displayed by default.

test_venv: run "-m pip" and "-m ensurepip._uninstall" with -W
ignore::DeprecationWarning since pip code is not part of Python.
diff --git a/Python/_warnings.c b/Python/_warnings.c
index d0f3941..8cfae76 100644
--- a/Python/_warnings.c
+++ b/Python/_warnings.c
@@ -1196,7 +1196,11 @@
 static PyObject *
 init_filters(void)
 {
+#ifndef Py_DEBUG
     PyObject *filters = PyList_New(5);
+#else
+    PyObject *filters = PyList_New(2);
+#endif
     unsigned int pos = 0;  /* Post-incremented in each use. */
     unsigned int x;
     const char *bytes_action, *resource_action;
@@ -1204,12 +1208,15 @@
     if (filters == NULL)
         return NULL;
 
+#ifndef Py_DEBUG
     PyList_SET_ITEM(filters, pos++,
                     create_filter(PyExc_DeprecationWarning, "ignore"));
     PyList_SET_ITEM(filters, pos++,
                     create_filter(PyExc_PendingDeprecationWarning, "ignore"));
     PyList_SET_ITEM(filters, pos++,
                     create_filter(PyExc_ImportWarning, "ignore"));
+#endif
+
     if (Py_BytesWarningFlag > 1)
         bytes_action = "error";
     else if (Py_BytesWarningFlag)