test_value.py: make `BoolValueTestCase` inherit `_TestNumericValue`

test_value.py: make `BoolValueTestCase` inherit `_TestNumericValue`

`BoolValue` is a numeric value, so `BoolValueTestCase` can inherit
`_TestNumericValue` and get more tests.

_inject_numeric_testing_methods() is also called on `BoolValueTestCase`
to test the different unary and binary operators.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I8fff73a0dda1e9ec9f6737739dde255c9b079ebf
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1586
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>