fix(server): enable regex crate unicode-perl feature

[mxinden]

Enable the unicode-perl feature flag on regex crate dependency in neqo-server crate.

The following regex makes use of the feature:

Regex::new(r"GET +/(\S+)(?:\r)?\n").unwrap()

Without the feature, the QUIC Interop tests panic with:

server  | thread 'main' panicked at neqo-server/src/old_https.rs:140:49:
server  | called `Result::unwrap()` on an `Err` value: Syntax(
server  | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
server  | regex parse error:
server  |     GET +/(\S+)(?:\r)?\n
server  |            ^^
server  | error: Unicode-aware Perl class not found (make sure the unicode-perl feature is enabled)
server  | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
server  | )

---

I will prioritize #1682 more to make sure we catch these regressions before merge.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.98%. Comparing base (a6bf979) to head (a28c68a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1714   +/-   ##
=======================================
  Coverage   92.98%   92.98%           
=======================================
  Files         120      120           
  Lines       37399    37399           
=======================================
  Hits        34775    34775           
  Misses       2624     2624           

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[mxinden]

Thanks @larseggert.

Can you trigger the QNS workflow on main so that https://interop.seemann.io/ eventually goes back to green?

https://github.com/mozilla/neqo/actions/workflows/qns.yml