Previously ALTER MATERIALIZED VIEW / FOREIGN TABLE ... RENAME COLUMN ...
returned "ALTER TABLE" as a command tag. This commit fixes them so that
they return "ALTER MATERIALIZED VIEW" and "ALTER FOREIGN TABLE" as
command tags, respectively.

This issue exists in all supported versions, but we don't back-patch this
because it's not enough of a bug to justify taking any compatibility risks for.
Otherwise, the back-patch would cause minor version update to break,
for example, the existing event trigger functions using TG_TAG.

Author: Fujii Masao
Reviewed-by: Ibrar Ahmed
Discussion: https://postgr.es/m/CAHGQGwGUaC03FFdTFoHsCuDrrNvFvNVQ6xyd40==P25WvuBJjg@mail.gmail.com