ci/test: fail on error

ci/test

@@ -5,11 +5,12 @@ bazel test "$@" ...
 
 # /tmp/bazel-zig-cc should be empty for the test below to be valid.
 # This test ensures that github.com/ziglang/zig/issues/13050 does not
-# regress from a "very high"-level perspective.
+# regress
 find /tmp/bazel-zig-cc -name mutex_destructor.o -execdir file {} \; | \
     sort | uniq -c | sort -rn > /tmp/got_cache
 
 diff -u ci/testdata/want_cache /tmp/got_cache || {
     >&2 echo "ERROR: unexpected artifacts."
     >&2 echo "Was /tmp/bazel-zig-cc empty before the test?"
+    exit 1
 }