fix(tests): Add shebangs, set -e, and comprehensive checks to Ubuntu test scripts

- Rewrite test_latest.sh with real tests for NVM, Node.js, pnpm, Bun, Deno, and version switching
- Add #!/bin/bash shebang and set -e to test_stable.sh and test_npmci.sh

test/test_stable.sh

@@ -1,3 +1,6 @@
+#!/bin/bash
+set -e
+
 # npm
 npm -v
 node -v