ci: move some tasks to background

- wkhtml download
- asset building
diff --git a/.github/helper/install.sh b/.github/helper/install.sh
index eab6d50..859146b 100644
--- a/.github/helper/install.sh
+++ b/.github/helper/install.sh
@@ -40,10 +40,14 @@
     echo "travis" | psql -h 127.0.0.1 -p 5432 -c "CREATE USER test_frappe WITH PASSWORD 'test_frappe'" -U postgres;
 fi
 
-wget -O /tmp/wkhtmltox.tar.xz https://github.com/frappe/wkhtmltopdf/raw/master/wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
-tar -xf /tmp/wkhtmltox.tar.xz -C /tmp
-sudo mv /tmp/wkhtmltox/bin/wkhtmltopdf /usr/local/bin/wkhtmltopdf
-sudo chmod o+x /usr/local/bin/wkhtmltopdf
+
+install_whktml() {
+    wget -O /tmp/wkhtmltox.tar.xz https://github.com/frappe/wkhtmltopdf/raw/master/wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
+    tar -xf /tmp/wkhtmltox.tar.xz -C /tmp
+    sudo mv /tmp/wkhtmltox/bin/wkhtmltopdf /usr/local/bin/wkhtmltopdf
+    sudo chmod o+x /usr/local/bin/wkhtmltopdf
+}
+install_whktml &
 
 cd ~/frappe-bench || exit
 
@@ -57,5 +61,5 @@
 if [ "$TYPE" == "server" ]; then bench setup requirements --dev; fi
 
 bench start &> bench_run_logs.txt &
+CI=Yes bench build --app frappe &
 bench --site test_site reinstall --yes
-bench build --app frappe