fix: add Ubuntu 26.04 support by converting GPG key to binary format

[vjripoll]

Summary

Adds support for Ubuntu 26.04 (Resolute) package installation testing.

Problem

Ubuntu 26.04 requires GPG keys in binary format instead of ASCII armored format (similar to Debian Trixie). When using ASCII armored keys, APT shows:

• The key(s) in the keyring /etc/apt/keyrings/newrelic-infra.gpg are ignored as the file has an unsupported filetype
  This caused package installation to fail with NO_PUBKEY errors.

Solution

Modified molecule/default/converge.yml to:

1. Convert GPG key to binary format using gpg --dearmor after repo setup
2. Update APT cache with the fixed key
3. Only applies to Ubuntu 26.04 via conditional when clause

The fix only executes when:

• ansible_distribution == "Ubuntu"
• ansible_distribution_version == "26.04"