Specify server certificate to use in SHA-1 test

Specify the SHA-1 server certificate to use in the SHA-1 test,
because now the default certificates use SHA256 certificates.
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index ae98ae9..5813305 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -3736,7 +3736,7 @@
 
 requires_gnutls
 run_test    "ClientHello without extensions, SHA-1 allowed" \
-            "$P_SRV debug_level=3" \
+            "$P_SRV debug_level=3 key_file=data_files/server2.key crt_file=data_files/server2.crt" \
             "$G_CLI --priority=NORMAL:%NO_EXTENSIONS:%DISABLE_SAFE_RENEGOTIATION" \
             0 \
             -s "dumping 'client hello extensions' (0 bytes)"