Build system: make Tor Browser tarball regexp stricter

config/chroot_local-hooks/10-tbb

@@ -337,7 +337,7 @@ TBB_TARBALLS="$(grep "\<tor-browser-linux64-.*\.tar.xz$" "${TBB_SHA256SUMS_FILE}
 
 # We'll use the en-US bundle as our basis; only langpacks will be
 # installed from the other bundles.
-MAIN_TARBALL="$(echo "${TBB_TARBALLS}" | grep -o "tor-browser-linux64-.*_en-US.tar.xz" || :)"
+MAIN_TARBALL="$(echo "${TBB_TARBALLS}" | grep -o "tor-browser-linux64-.*_en-US\.tar\.xz" || :)"
 NIGHTLY_BUILD=
 if [ -z "${MAIN_TARBALL}" ] && [ "$(echo $TBB_TARBALLS | awk '{ print $2 }')" = 'tor-browser-linux64-tbb-nightly_ALL.tar.xz' ]; then
     # Except for TBB nightly builds; then there is only one bundle