Fix debtap package database check to support updated pkgfile cache filenames

[Laksh-Mendpara]

PR Description:
This PR addresses an issue where debtap fails with the misleading error:
"Error: You must run at least once 'debtap -u' with root privileges..."
even when debtap -u has already been run successfully.

Problem:
Github Issue - #92

Fix:
Replaced the strict glob pattern with a more flexible expression using grep -E:

if [[ ! $(ls /var/cache/pkgfile 2> /dev/null | grep -E '.*\.files(\.[[:digit:]]{3})?') ]] ...

This allows the check to recognize both unsuffixed and suffixed .files entries.

Notes:

• Ensures compatibility with updated versions of pkgfile that store cache files with numeric suffixes.
• Only affects the initial environment check; other parts of debtap are unaffected.
• Solves the issue for systems using the new cache structure.