switching from yarn to pnpm

scripts/playwright-webserver-command.sh

@@ -1,10 +1,10 @@
 #!/bin/sh
 if [ -n "$USE_DOCKER" ]; then
     set -ex
-    yarn build
+    pnpm build
     docker build -t element-call:testing .
     exec docker run --rm --name element-call-testing -p 8080:8080 -v ./config/config.devenv.json:/app/config.json:ro,Z element-call:testing
 else
     cp config/config.devenv.json public/config.json
-    exec yarn dev
+    exec pnpm dev
 fi