Bug in regex used to detect robots noindex directive in page header

[cicirello]

Summary

The current regular expression used to detect if there is a meta tag in the page header with a robots noindex directive (e.g., to exclude such pages from the sitemap) has a potential bug. \s* is used in a couple places to account for sequences of space characters. However, it is not being passed through to Python's regular expression processor, and instead being detected as an invalid escape sequence in the string. Need to escape the \. Revealed when upgrading to Python 3.12, which gives a warning. Earlier versions of Python not warning on this, although behavior appears to be correct. Not entirely sure why. But should fix this none-the-less.