tests: add b'' when testing for tls1.2

The dict keys are bytes. The test was always failing due to
looking for a str key.

skip-blame: just b'' prefix

Differential Revision: https://phab.mercurial-scm.org/D5701

tests/hghave.py

@@ -543,7 +543,7 b' def has_defaultcacertsloaded():'
 @check("tls1.2", "TLS 1.2 protocol support")
 def has_tls1_2():
     from mercurial import sslutil
-    return 'tls1.2' in sslutil.supportedprotocols
+    return b'tls1.2' in sslutil.supportedprotocols
 
 @check("windows", "Windows")
 def has_windows():