tests: refresh devtools checkout for webtests (#11717)

lighthouse-core/test/chromium-web-tests/download-devtools.sh

@@ -12,6 +12,11 @@ if [ -d "$DEVTOOLS_PATH" ]
 then
   echo "Directory $DEVTOOLS_PATH already exists."
   cd "$DEVTOOLS_PATH"
+
+  # Update to keep current
+  git pull -f origin master
+  gclient sync
+
   exit 0
 fi
 
@@ -27,4 +32,4 @@ cd devtools-frontend
 gclient sync
 gn gen out/Default
 
-set +x
+set +x