[SYCL] Disable PI unit tests by default (intel#10781)

These tests are currently disabled in the CI and ended up broken.

Since we're also currently moving to the Unified Runtime we might be
able to replace most of them with the Unified Runtime CTS, or they will
also need to be ported to the Unified Runtime.

So disable them by default until we figure out a proper course of action
of these.

Related ticket: intel#10688

sycl/unittests/CMakeLists.txt

@@ -27,7 +27,7 @@ include(AddSYCLUnitTest)
 add_custom_target(check-sycl-unittests)
 
 # TODO PI tests require real hardware and must be moved to sycl/test-e2e.
-option(SYCL_PI_TESTS "Enable PI-specific unit tests" ON)
+option(SYCL_PI_TESTS "Enable PI-specific unit tests" OFF)
 
 if (SYCL_PI_TESTS)
   add_subdirectory(pi)