allocators: Fix manual ABI test
Fixing this build error:
In file included from tests/layout.c:6:
tests/manual.h:3:10: fatal error: gst/base/base.h: No such file or directory
3 | #include <gst/base/base.h>
| ^~~~~~~~~~~~~~~~~
compilation terminated.
test cross_validate_layout_with_c ... FAILED
In file included from tests/constant.c:6:
tests/manual.h:3:10: fatal error: gst/base/base.h: No such file or directory
3 | #include <gst/base/base.h>
| ^~~~~~~~~~~~~~~~~
Edited by Philippe Normand