Force TLS version to 1.2 when using LibreSSL

This comment previously specified TLS 1.2, but actually set the
version to TLS 1.0.  LibreSSL 3.8.1 (included in OpenBSD 7.4)
dropped support for TLS 1.0/1.1 for security reasons, which
broke this test.  Switch the test to use TLS 1.2 as documented
so it will continue to work on OpenBSD 7.4+.

test/net/http/test_https.rb

@@ -148,7 +148,7 @@ def test_session_reuse
       # support session resuse.  Limiting the version to the TLSv1.2 stack allows
       # this test to continue to work on LibreSSL 3.2+.  LibreSSL may eventually
       # support session reuse, but there are no current plans to do so.
-      http.ssl_version = :TLSv1
+      http.ssl_version = :TLSv1_2
     end
 
     http.start