HTAB (\t) are not allowed in header values when using httptools

[jhominal]

The regular expression to validate header values is [\x00-\x1F\x7F]

However, RFC 9110, section 5.5 allows both spaces (0x20) and horizontal tabs (0x09). However, the regular expression above will erroneously detect \x09 as being invalid.

For that reason, I think that the regular expression should be amended to allow horizontal tabs.

As a comparison basis, note that h11 allows \t character in header values: https://github.com/python-hyper/h11/blob/cc87dfcc5a4693eb49b0453e6677ca004ffb035b/h11/_abnf.py#L57

[Kludex]

PR welcome

[jhominal]

#2345 :)