tests: always distribute strace-k.test

Fix distribution of tests/strace-k.test file when configured
without libunwind.

* tests/Makefile.am (EXTRA_DIST): Add strace-k.test.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index dcc9323..5b5a72e 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -706,6 +706,7 @@
 	     statx.sh \
 	     strace-T.expected \
 	     strace-ff.expected \
+	     strace-k.test \
 	     strace-r.expected \
 	     struct_flock.c \
 	     sun_path.expected \