docs/devel/testing.rst: Fix references to unit tests

With the recent move of the unit tests to tests/unit directory some
instructions under the "Unit tests" section became imprecise, which
are fixed by this change.

Fixes: da668aa15b99 ("tests: Move unit tests into a separate directory")
Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20210318174407.2299930-1-wainersm@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

docs/devel/testing.rst

@@ -34,17 +34,17 @@ If you are writing new code in QEMU, consider adding a unit test, especially
 for utility modules that are relatively stateless or have few dependencies. To
 add a new unit test:
 
-1. Create a new source file. For example, ``tests/foo-test.c``.
+1. Create a new source file. For example, ``tests/unit/foo-test.c``.
 
 2. Write the test. Normally you would include the header file which exports
    the module API, then verify the interface behaves as expected from your
    test. The test code should be organized with the glib testing framework.
    Copying and modifying an existing test is usually a good idea.
 
-3. Add the test to ``tests/meson.build``. The unit tests are listed in a
+3. Add the test to ``tests/unit/meson.build``. The unit tests are listed in a
    dictionary called ``tests``.  The values are any additional sources and
    dependencies to be linked with the test.  For a simple test whose source
-   is in ``tests/foo-test.c``, it is enough to add an entry like::
+   is in ``tests/unit/foo-test.c``, it is enough to add an entry like::
 
      {
        ...