Fix: Prevent partial directory matching in change detection

[bijantavakoli]

Fixes a bug where directory names that are substrings of others (e.g., shopify_general vs shopify_general_v2) caused false positive builds.

The logic has been updated to strictly enforce directory boundaries (using path.sep) so that changes in a _v2 folder do not trigger builds for the base folder.

Please see the Issue for more details: #30

[nafarlee]

This PR and your corresponding issue seem correct on the merits. However, this action has gone unmaintained for years, due in part to our recommendation shifting overtime:

• If you are building in response to file changes, colpal/actions-changed-files was deprecated in favor of tj-actions/changed-files. tj-actions/changed-files has native support for creating parallel matrix configurations, thus allowing this kind of parallel Docker image building to happen across multiple runners and be more flexible in definition
• If you are just trying to do batch builds regardless of changes, the same approach as above can be used, but with [colpal/actions-find-exec](https://github.com/colpal/actions-find-exec) as a "glob" interface

I think it best for current users of colpal/actions-batch-docker to migrate to one of the approaches above. I don't mind merging this PR and releasing a new version...but it might not be worth putting any additional time into maintaining/using this action