[node_preamble] Update pubspec to 3.7.

No reformatting required.

Change-Id: I0525d93f8d314b65db43e0bbccdfed45ff41711b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/400761
Commit-Queue: Sigmund Cherem <[email protected]>
Auto-Submit: Mayank Patke <[email protected]>
Reviewed-by: Sigmund Cherem <[email protected]>

Author: fishythefish

pkg/node_preamble/pubspec.yaml

@@ -1,5 +1,5 @@
 # This is just a stub, not the real node_preamble package
 name: node_preamble
 environment:
-  sdk: ^3.5.0
+  sdk: ^3.7.0-0
 publish_to: none