run gate tests on "fast" machines

ci.hocon

@@ -136,8 +136,8 @@ rbcheck : ${common} {
 # The standard set of gate builds. N.B. the style/builtin checks are only run on Linux as they are not OS-dependent.
 
 builds = [
-  ${gateTestLinux}            {capabilities : [linux, amd64],  targets : [gate, post-merge], name: "gate-test-linux-amd64"}
-  ${gateTestNoSpecialsLinux}  {capabilities : [linux, amd64],  targets : [gate, post-merge], name: "gate-test-linux-amd64-nospecials"}
+  ${gateTestLinux}            {capabilities : [linux, amd64, fast],  targets : [gate, post-merge], name: "gate-test-linux-amd64"}
+  ${gateTestNoSpecialsLinux}  {capabilities : [linux, amd64, fast],  targets : [gate, post-merge], name: "gate-test-linux-amd64-nospecials"}
   ${gateTestDarwin}           {capabilities : [darwin, amd64], targets : [gate, post-merge], name: "gate-test-darwin-amd64"}
   ${gateStyle}                {capabilities : [linux, amd64],  targets : [gate, post-merge], name: "gate-style-linux-amd64"}
   ${rbcheck}                  {capabilities : [linux, amd64],  targets : [gate, post-merge], name: "gate-rbcheck-linux-amd64"}