execve: Move KUnit tests to tests/ subdirectory

Move the exec KUnit tests into a separate directory to avoid polluting
the local directory namespace. Additionally update MAINTAINERS for the
new files.

Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Acked-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20240720170310.it.942-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

MAINTAINERS

@@ -8220,7 +8220,8 @@ F:	Documentation/userspace-api/ELF.rst
 F:	fs/*binfmt_*.c
 F:	fs/Kconfig.binfmt
 F:	fs/exec.c
-F:	fs/exec_test.c
+F:	fs/tests/binfmt_*_kunit.c
+F:	fs/tests/exec_kunit.c
 F:	include/linux/binfmts.h
 F:	include/linux/elf.h
 F:	include/uapi/linux/binfmts.h

fs/binfmt_elf.c

@@ -2152,5 +2152,5 @@ core_initcall(init_elf_binfmt);
 module_exit(exit_elf_binfmt);
 
 #ifdef CONFIG_BINFMT_ELF_KUNIT_TEST
-#include "binfmt_elf_test.c"
+#include "tests/binfmt_elf_kunit.c"
 #endif

fs/exec.c

@@ -2244,5 +2244,5 @@ fs_initcall(init_fs_exec_sysctls);
 #endif /* CONFIG_SYSCTL */
 
 #ifdef CONFIG_EXEC_KUNIT_TEST
-#include "exec_test.c"
+#include "tests/exec_kunit.c"
 #endif