ci: skip flakey darwin tests on PR runs (#4749)

Some care has been taken that these tests still run on development
machines. They'll only be skipped if the following is true:

1. the os is darwin
2. the GITHUB_ACTIONS env var is set to something

This approach, adding the skip calls manually on a case-by-case basis,
should allow us some fine-grained control. If we had used build tags,
we'd only be able to skip all the tests in one file together.

Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>

util/test/ci_skip.go

@@ -0,0 +1,10 @@
+//go:build !darwin
+// +build !darwin
+
+package test
+
+import "testing"
+
+// Skip will skip this test on pull request CI runs.
+// Used for slow test runners on GHA's darwin machines.
+func Skip(*testing.T) {}

util/test/ci_skip_darwin.go

@@ -0,0 +1,15 @@
+package test
+
+import (
+	"os"
+	"testing"
+)
+
+// Skip will skip this test on pull request CI runs.
+// Used for slow test runners on GHA's darwin machines.
+func Skip(t *testing.T) {
+	if os.Getenv("GITHUB_ACTIONS") == "" {
+		return
+	}
+	t.Skip("skipped on Darwin, test runner is slow")
+}