Fixes <https://bugs.gnu.org/40582>.
Reported by Julien Lepiller <julien@lepiller.eu>.
Previously, a host part consisting of hex digits would be mistaken as an
IPv6 address and rejected by 'valid-host?'.
* module/web/uri.scm (ipv6-regexp): Add colon.
* test-suite/tests/web-uri.test ("string->uri")["xyz://abc/x/y/z"]: New
test.
* NEWS: Update.