Fix network failure handling in install-wp-tests.sh update check

[Copilot]

The download() function doesn't return error codes, allowing network failures to silently pass through. The check_for_updates() function could then process empty or invalid files, leading to false negatives in update detection.

Changes

• download() function: Added explicit return $? to propagate curl/wget exit codes
• check_for_updates() function:
  • Check download return value with if ! download ...
  • Validate downloaded file is non-empty with -s flag
  • Separate error messages for network failures vs. empty files

Before

download "$remote_url" "$tmp_script"

if [ ! -f "$tmp_script" ]; then
    echo -e "${YELLOW}Warning: Could not download...${RESET}"
    return
fi

After

if ! download "$remote_url" "$tmp_script"; then
    echo -e "${YELLOW}Warning: Failed to download...${RESET}"
    return
fi

if [ ! -f "$tmp_script" ] || [ ! -s "$tmp_script" ]; then
    echo -e "${YELLOW}Warning: Downloaded script is missing or empty...${RESET}"
    rm -f "$tmp_script"
    return
fi

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• invalid-domain-that-does-not-exist-12345.com
  • Triggering command: /usr/bin/curl curl -L -s REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)