models: also count test_regression collection
models: also count test_regression collection

Enable count queries for the test_regresion collection.  This is in
particular useful for showing the number of regressions associated
with a set of test results.

Signed-off-by: Guillaume Tucker <e7e20b7c30f19d4ca6b81319ef81bf200369d137@collabora.com>

kernelci/kernelci-backend,kernelci/kernelci-backend