Fix token fallback in add-files-changed-label workflow

[Copilot]

The workflow fails with "Bad credentials" (401) when fetching repository labels because the token fallback expression evaluates incorrectly when CUSTOM_GITHUB_TOKEN is undefined.

Changes

• Fix token assignment in .github/workflows/add-files-changed-label.yml to properly check for token existence before fallback

Before:

GITHUB_TOKEN: ${{ secrets.CUSTOM_GITHUB_TOKEN || secrets.GITHUB_TOKEN }}

After:

GITHUB_TOKEN: ${{ secrets.CUSTOM_GITHUB_TOKEN != '' && secrets.CUSTOM_GITHUB_TOKEN || github.token }}

The || operator doesn't handle undefined secrets correctly. The fixed expression explicitly checks if CUSTOM_GITHUB_TOKEN exists before using it, otherwise falls back to github.token (the built-in Actions token).

Original prompt

fix github action to add file count - Run echo "Starting Files Changed Label workflow for PR #$PR_NUMBER in $REPO_OWNER/$REPO_NAME"
##[debug]/usr/bin/bash -e /home/runner/work/_temp/13151e4e-0a01-4a02-b754-050b7eda6cfb.sh
Starting Files Changed Label workflow for PR #4666 in OWASP-BLT/BLT
Fetching files changed information...
Files changed in PR #4666: 3
Determined label: files-changed: 3 with color: fbca04
Checking if label exists in repository...
Error: Failed to fetch repository labels. Response: {
"message": "Bad credentials",
"documentation_url": "https://docs.github.com/rest",
"status": "401"
}

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