Fix *.out file path in integration tests documentation (godotengine#8221)

The path to the `bin/` directory is written from the root as `./bin/<godot_binary>`,
however the path to the `scripts/` directory is written from outside the root as
`godot-source/modules/gdscript/tests/scripts`, which is inconsistent.

Author: k0T0z

contributing/development/core_and_modules/unit_testing.rst

@@ -319,18 +319,24 @@ Therefore, the process of writing integration tests for GDScript is the followin
             if true # Missing colon here.
                 print("true")
 
-3. Generate ``*.out`` files to update the expected results from the output:
+3. Change directory to the Godot source repository root.
 
    .. code-block:: shell
 
-       ./bin/<godot_binary> --gdscript-generate-tests godot-source/modules/gdscript/tests/scripts
+       cd godot
+
+4. Generate ``*.out`` files to update the expected results from the output:
+
+   .. code-block:: shell
+
+       bin/<godot_binary> --gdscript-generate-tests modules/gdscript/tests/scripts
 
 You may add the ``--print-filenames`` option to see filenames as their test
 outputs are generated. If you are working on a new feature that is causing
 hard crashes, you can use this option to quickly find which test file causes
 the crash and debug from there.
 
-4. Run GDScript tests with:
+5. Run GDScript tests with:
 
    .. code-block:: shell