do not test metrics collector under ARC

chroprof.nimble

@@ -12,4 +12,6 @@ requires  "nim >= 1.6.16",
           "metrics >= 0.1.0"
 
 task test, "Run tests":
-  exec "nim c --out:./build/testall -r tests/testall.nim"
+  exec "nim c --out:./build/testall -r tests/testall.nim"
+  # nim-metrics doesn't play well with ARC
+  exec "nim c --out:./build/testall --mm:refc -d:metrics -r tests/testall.nim"

tests/config.nims

@@ -1,3 +1,2 @@
 switch("threads", "on")
 switch("define", "chronosProfiling")
-switch("define", "metrics")

tests/testall.nim

@@ -1,3 +1,6 @@
-import ./[testevents, testmetricscollector, testprofiler]
+import ./[testevents, testprofiler]
+
+when defined(metrics):
+  import ./testmetricscollector
 
 {.warning[UnusedImport]: off.}