Update Firefox version in DEPS to 131.0

Change-Id: Ie3ac8ebbc1bbcb72cf122f831a5625a7b5f3ca03
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/387761
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>
Commit-Queue: Srujan Gaddam <srujzs@google.com>
Auto-Submit: Nate Biggs <natebiggs@google.com>

DEPS

@@ -207,7 +207,7 @@ vars = {
   "download_chrome": False,
   "chrome_tag": "130.0.6723.6",
   "download_firefox": False,
-  "firefox_tag": "130.0.1",
+  "firefox_tag": "131.0",
 
   # Emscripten is used in dart2wasm tests.
   "download_emscripten": False,