Update canvaskit version and change get to upgrade.

tool/build_release.sh

diff --git a/tool/build_release.sh b/tool/build_release.sh
index 4369fd4..ad9c6e1 100755
--- a/tool/build_release.sh
+++ b/tool/build_release.sh
@@ -14,7 +14,7 @@
 # (https://github.com/flutter/flutter/issues/74936), or to read this from a manifest 
 # provided (https://github.com/flutter/flutter/issues/74934).
 function download_canvaskit() {
-  local canvaskit_url=https://unpkg.com/canvaskit-wasm@0.25.1/bin/
+  local canvaskit_url=https://unpkg.com/canvaskit-wasm@0.26.0/bin/
 
   local flutter_bin=$(which flutter)
   local canvaskit_dart_file=$(dirname $flutter_bin)/cache/flutter_web_sdk/lib/_engine/engine/canvaskit/initialization.dart
@@ -38,7 +38,7 @@
 
 download_canvaskit
 
-flutter pub get
+flutter pub upgrade
 
 # Build a profile build rather than a release build to avoid minification
 # as code size doesn't matter very much for us as minification makes some