Update invoice-ninja to version v5.11.6

[nmfretz]

🤖 This is an automated pull request to update invoice-ninja to version v5.11.6. This PR must be reviewed and tested before merging.

[nmfretz]

🤖 This is an automated summary of installation tests for invoice-ninja:

• ✅ App successfully installed in umbrel-dev instance
• ❌ App not listed in umbrel.yaml
• ⚠️ App UI accessibility was not tested

This PR must still be reviewed and tested before merging.

[github-actions]

❌   Linting failed with 1 error   ❌

Thank you for your submission! This is an automated linter that checks for common issues in pull requests to the Umbrel App Store.

Please review the linting results below and make any necessary changes to your submission.

Linting Results

Severity	File	Description
❌	invoice-ninja/docker-compose.yml	Invalid image name "mariadb:10.5.12@sha256:dfcba5641bdbfd7cbf5b07eeed707a6a3672f46823695a0d3aba2e49bbd9b1dd": Error: HTTP 404 for mariadb:10.5.12@sha256:dfcba5641bdbfd7cbf5b07eeed707a6a3672f46823695a0d3aba2e49bbd9b1dd: {"errors":[{"code":"MANIFEST_UNKNOWN","message":"manifest unknown","detail":"unknown manifest name=library/mariadb revision=sha256:dfcba5641bdbfd7cbf5b07eeed707a6a3672f46823695a0d3aba2e49bbd9b1dd"}]}
ℹ️	invoice-ninja/docker-compose.yml	Potentially using unsafe user in service "nginx": The default container user "root" can lead to security vulnerabilities. If you are using the root user, please try to specify a different user (e.g. "1000:1000") in the compose file or try to set the UID/PUID and GID/PGID environment variables to 1000.

Legend

Symbol	Description
❌	Error: This must be resolved before this PR can be merged.
⚠️	Warning: This is highly encouraged to be resolved, but is not strictly mandatory.
ℹ️	Info: This is just for your information.