Add a comment for no_check_targets in //.gn.

Reference the relevant V8 bug and remind readers to check if the same GN
issues have been fixed in Chromium.

Change-Id: I4942ae4f0f1e0f3bcf1a2d4a76d694a8e225fcb5
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/102051
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: Nigi <nigi@chromium.org>
diff --git a/.gn b/.gn
index 59da479..9d6330b 100644
--- a/.gn
+++ b/.gn
@@ -21,6 +21,8 @@
 }
 
 no_check_targets = [
+  # See https://crbug.com/v8/7330 and/or check if these entries exist in
+  # Chromium's //.gn file.
   "//v8:cppgc_base",
   "//v8:v8_internal_headers",
   "//v8/src/inspector:inspector",