pw_assert_log: add missing check_backend.impl group

Bugfix, this was missing from this change:
https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/96741

Change-Id: I3fa2f73c924d637b502ed62df4b8beb8389f195e
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/97908
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>
diff --git a/pw_assert_log/BUILD.gn b/pw_assert_log/BUILD.gn
index a5fa0b8..714fb1f 100644
--- a/pw_assert_log/BUILD.gn
+++ b/pw_assert_log/BUILD.gn
@@ -79,6 +79,9 @@
 group("assert_backend.impl") {
 }
 
+group("check_backend.impl") {
+}
+
 # pw_assert_log doesn't have deps with potential circular dependencies, so this
 # impl group can be empty.
 group("pw_assert_log.impl") {