R packages: don't match packages with unrequested suffixes

This fixes the issue where a request for "spatstat" would match "r-cran-spatstat.core" when autodep8 is run on a bookworm system for testing on a trixie/sid system where that package no longer exists.

(Other, less problematic, and yet still unneeded packages would also match: r-cran-spatstat.data, r-cran-spatstat.explore, r-cran-spatstat.geom, r-cran-spatstat.linnet, r-cran-spatstat.model, r-cran-spatstat.random, r-cran-spatstat.sparse, r-cran-spatstat.utils)

Releasing and deploying a new autodep8 with this fix will eventually allow us to close https://bugs.debian.org/1071106 https://bugs.debian.org/1069051 and unstick other testing migrations.

This is a partial fix for https://bugs.debian.org/961138