Bump hypothesis version in requirements-dev.txt

The problem: in two tests ("test_connect_where_client_times_out" and
"test_connect_to_whitelisted_slow_upstream_host"), the @given decorator
did not pass the "autojump_clock" fixture.

Version 6.49.1 seems to fix this. At a glance, it seems that Hypothesis
did not allow @given to wrap functions with positional-only arguments...
but it still worked with "test_cancellation_seen_promptly", which also
used the "autojump_clock" fixture. The difference is the first two were
also decorated with my @resolve_all_to_localhost decorator.

This might be interesting to look into later.

requirements-dev.txt

@@ -1,5 +1,5 @@
 trio==0.21.0
 h11==0.14.0
-hypothesis==6.46.7
+hypothesis==6.49.1
 pytest==7.1.2
 pytest-trio==0.7.0