REGTESTS: Replace REQUIRE_VERSION=2.5 with 'haproxy -cc'

This is safe, because running `haproxy -cc 'version_atleast(2.5-dev0)'` on
HAProxy 2.4 will also result in an exit code of 1.
diff --git a/reg-tests/ssl/set_ssl_cafile.vtc b/reg-tests/ssl/set_ssl_cafile.vtc
index eb62563..2f4ef2e 100644
--- a/reg-tests/ssl/set_ssl_cafile.vtc
+++ b/reg-tests/ssl/set_ssl_cafile.vtc
@@ -15,7 +15,7 @@
 # - Check that you have socat
 
 varnishtest "Test the 'set ssl ca-file' feature of the CLI"
-#REQUIRE_VERSION=2.5
+feature cmd "$HAPROXY_PROGRAM -cc 'version_atleast(2.5-dev0)'"
 #REQUIRE_OPTIONS=OPENSSL
 #REQUIRE_BINARIES=socat
 feature ignore_unknown_macro