internal/crashmonitor: clarify pre-go1.23 behavior

The current comment implies that traceback includes PCs for inlined
frames in 1.23, which is not the case.

For golang/go#70637.

Change-Id: I26fe4328843733d230e31ccdb452d4a25ae91b3c
Reviewed-on: https://go-review.googlesource.com/c/telemetry/+/637756
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

internal/crashmonitor/monitor_test.go

@@ -89,7 +89,13 @@ func TestViaStderr(t *testing.T) {
 		"runtime.goexit:--"
 
 	if !crashmonitor.Supported() { // !go1.23
-		// Before go1.23, the traceback excluded PCs for inlined frames.
+		// Traceback excludes PCs for inlined frames. Before go1.23
+		// (https://go.dev/cl/571798 specifically), passing the set of
+		// PCs in the traceback to runtime.CallersFrames, would report
+		// only the innermost inlined frame and none of the inline
+		// "callers".
+		//
+		// Thus, here we must drop the caller of the inlined frame.
 		want = strings.ReplaceAll(want, "golang.org/x/telemetry/internal/crashmonitor_test.child:+2\n", "")
 	}