Tighten up phan type for ContentRenderer::getParserOutput()
Passing an int as the $revision was deprecated with a warning, but
also tighten up the phan @param type to hopefully catch a few more
cases of this in CI rather than the logs.
Bug: T350538
Bug: T358243
Change-Id: I73a3b77d9982bcfaa9c235cde31fafff9a13e92e