Update build files and GitHub Actions workflow

.github/actions/import-assets/action.yml

@@ -0,0 +1,10 @@
+name: Import assets
+runs:
+  using: "composite"
+  steps:
+    - name: Import assets
+      shell: bash
+      run: |
+        # HACK: See https://github.com/godotengine/godot-proposals/issues/1362.
+        (for i in {1..4}; do godot --editor --headless & sleep 5 && .github/actions/import-assets/monitor_import.sh; done) || true
+

.github/actions/import-assets/monitor_import.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+# Source: https://github.com/godotengine/godot/pull/68461#issuecomment-1328177902
+
+while [ "$(printf "%.0f\n" $(top -n 1 -b | awk '/^%Cpu/{print $2}'))" -gt 10 ];
+do
+echo "$(top -n 1 -b | awk '/^%Cpu/{print $2}')";
+done
+echo "Finished importing. Killing godot editor process";
+kill -9 $(pgrep -o godot)