tests: Pass right type/width to varargs TrackerBatch API
We specify G_TYPE_INT64 but pass an unspecified integer that gets promoted to 32-bit. This wreaks havoc in the GValue varargs collection glib code.
Specify the right type in our tests, so that we don't hit this bug.
Closes: #397 (closed)
Note: Currently includes !586 (merged), to verify that CI does pass