Update Chrome and Firefox versions.

Chrome: 137.0.7151.40
Firefox: 138.0.4
Change-Id: I9251c10255fa86da8ad710757de324fb1e6cd678
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/430840
Reviewed-by: Mark Zhou <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>

Author: natebiggs

DEPS

@@ -160,9 +160,9 @@ vars = {
   # meant to be downloaded by users for local testing. You can self-service
   # update these by following the go/dart-engprod/browsers.md instructions.
   "download_chrome": False,
-  "chrome_tag": "137.0.7151.15",
+  "chrome_tag": "137.0.7151.40",
   "download_firefox": False,
-  "firefox_tag": "138.0",
+  "firefox_tag": "138.0.4",
 
   # Emscripten is used in dart2wasm tests.
   "download_emscripten": False,