ci: fix docs-only filter to properly skip tests for documentation changes

[blackgirlbytes]

Fix CI workflow to properly skip tests for documentation-only changes

Problem

The current CI workflow runs all tests even for documentation-only PRs (like #4004), despite having a changes job intended to detect and skip these scenarios.

Root Cause

The code filter uses '**' as an inclusion pattern, which causes it to evaluate to true whenever any files are changed, regardless of the exclusion patterns that follow:

code:
  - '**'                    # Matches all files (always true if any files changed)
  - '!documentation/**'     # Exclusions don't prevent the filter from being true
  - '!**/*.md'

Solution

Remove the '**' pattern and use only exclusion patterns for the code filter. Also expand markdown detection to include subdirectories:

docs-only:
  - 'documentation/**'
  - '**/*.md'              # Matches .md files anywhere in repo
code:
  - '!documentation/**'    # Only true if non-documentation files are changed
  - '!**/*.md'

Result

• Documentation-only PRs will have code = false, properly skipping expensive CI jobs
• Markdown files anywhere in the repo (README files, etc.) are treated as documentation
• Code changes still trigger full CI as expected

Testing

This change would have prevented the unnecessary CI runs on PR #4004, which only modified files under documentation/blog/.

Tested on my forked PR

Docs change

Skipped the other unneeded build test

Code change

Included the other build test