ci: further reduce unnecessary push runs

[Saviq]

What's new?

SymbolsCheck is required on merge queue, no need to run on main.
Metadata files don't impact packaging or tests.

How to test

Can't…

Checklist

• Tests added and pass
• Adequate documentation added
• (optional) Added Screenshots or videos

[Copilot]

Pull request overview

This PR updates GitHub Actions workflow triggers to avoid running certain CI jobs on pushes when changes are limited to non-functional repository files, and limits when Symbols Check runs.

Changes:

• Add additional paths-ignore entries (*.md, COPYING.*, and spread.yaml in one workflow) to reduce push-triggered workflow runs.
• Remove the push trigger for Symbols Check, leaving it to run on merge_group and pull_request.
• Add a Renovate configuration file under .github/.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
.github/workflows/tics.yml	Skip push runs when only top-level markdown/license files change.
.github/workflows/symbols-check.yml	Stop running Symbols Check on pushes to main.
.github/workflows/spread.yml	Skip push runs when only top-level markdown/license files change.
.github/workflows/ppa-upload.yml	Skip push runs when only top-level markdown/license/spread config files change.
.github/renovate.json	Introduce Renovate bot configuration.