Clarify that Xcode issues are not tracked in BUG_REPORT.yml (#7324)

We're seeing a large amount of issues created that are unrelated to this
repository. We need to add a clear warning to our issue template that
such issues will be closed.

Author: MaxDesiatov

.github/ISSUE_TEMPLATE/BUG_REPORT.yml

@@ -2,6 +2,14 @@ name: Bug Report
 description: Something isn't working as expected
 labels: [bug]
 body:
+- type: checkboxes
+  id: cat-preferences
+  attributes:
+    label: "Is it reproducible with SwiftPM command-line tools: `swift build`, `swift test`, `swift package` etc?"
+    description: "Issues related to closed-source software are not tracked by this repository and will be closed. For Xcode, please file a feedback at https://feedbackassistant.apple.com instead."
+    options:
+      - label: Confirmed reproduction steps with SwiftPM CLI. 
+        required: true
 - type: textarea
   attributes:
     label: Description