build: Fix configure error in tracker_core=subproject mode

Fixes the following error from Meson:

    ../meson.build:459:21: ERROR: Unknown variable "tracker_sparql_uninstalled_dir".

Nothing changed recently here but it looks like we didn't correctly
query that variable from the 'tracker' subproject, relying on it being
implicitly available. With Meson 0.55.3 this wasn't working, but perhaps
it worked with earlier versions.
5 jobs for sam/meson-subproject-build-fail in 23 minutes and 22 seconds
latest
Status Job ID Name Coverage
  Test
passed #1354338
test-fedora-latest

00:04:54

passed #1354339
test-fedora-rawhide

00:04:51

passed #1354393
test-ubuntu-rolling

00:08:58

failed #1354340
test-ubuntu-rolling

00:05:45

 
  Analysis
passed #1354341
coverage-analysis

00:09:29

49.5%