Update chrome and firefox versions to 138.0.7204.23 and 139.0.4 respectively.

Change-Id: I651050255bea41eea9c36727b0b7920311639c8c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/434440
Reviewed-by: Srujan Gaddam <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>

Author: natebiggs

DEPS

@@ -161,9 +161,9 @@ 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": "138.0.7204.4",
+  "chrome_tag": "138.0.7204.23",
   "download_firefox": False,
-  "firefox_tag": "139.0",
+  "firefox_tag": "139.0.4",
 
   # Emscripten is used in dart2wasm tests.
   "download_emscripten": False,