Umbrel v0.2.15

This update fixes some compatibility issues between Umbrel and the latest version of Electrum Wallet.

Changes:

• Ensure PR builds run against the correct commit (#273) e9e2611 (@AaronDewes)
• Remove use of deprecated ::set-env in GitHub Actions (#316) b7416dc (@AaronDewes)
• Prevent LND from rotating TLS cert every startup (#318) a627fdf (@louneskmt)
• Update to getumbrel/electrs:v0.8.6 (#321) 6b28d84 (@lukechilds)

Diff: v0.2.14...v0.2.15