[suppressions] Use path.resolve() instead of path.join() on suppression paths

https://github.com/Azure/azure-rest-api-specs/blob/959652aca6777cd5db6fd792be4e52dfbaa122ef/eng/tools/suppressions/src/suppressions.ts#L170-L173

L171 should use `path.resolve()` instead of `path.join()`. They are usually the same, but diverge if the second argument is an absolute path. The behavior of `resolve()` is more appropriate here.

```
> path.join("/home/specs", "foo/bar")
'/home/specs/foo/bar'
> path.resolve("/home/specs", "foo/bar")
'/home/specs/foo/bar'

> path.join("/home/specs", "/foo/bar")
'/home/specs/foo/bar'
> path.resolve("/home/specs", "/foo/bar")
'/foo/bar'
```