don't build the tests for acquire test dependencies (acquire-project#83)

This resolves a failure to build tests that we're currently experiencing
on main.

Tests pull in acquire libraries (like `acquire-driver-common` and
`acquire-video-runtime`) as dependencies. These are brought in as
submodules and compiled with the tests.

Doing things this way, also causes the tests in the dependencies. That
can be nice because we make sure the dependencies are running correctly,
but it introduces all kinds of build shenanigans and is somewhat
wasteful. We tend to have good observability on whether the dependencies
are working anyway.

So this PR uses the `NOTEST` variable in the `test/CMakeLists.txt` to
turn off the building of tests in dependencies.

tests/CMakeLists.txt

@@ -1,8 +1,10 @@
 if(${NOTEST})
     message(STATUS "Skipping test targets")
 else()
+    set(NOTEST "TRUE")
     aq_require(acquire-video-runtime)
     aq_require(acquire-driver-common)
+    set(NOTEST "FALSE")
 
     #
     # PARAMETERS