Add json-c as unit test build dependency

nbd-proxy.c needs json-c as dependency - CI run fails on that.

Added latest tagged git version (json-c-0.16-2022041) the same as in
the OpenBMC.

Tested:
locally passed run-unit-test-docker.sh on jsnbd repository.

Change-Id: I837247a2c4b9ebee3081cea3adae68364da269f9
Signed-off-by: Przemyslaw Czarnowski <przemyslaw.hawrylewicz.czarnowski@intel.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index b09cd5e..0d60de0 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -146,6 +146,10 @@
             ),
         ],
     ),
+    "json-c/json-c": PackageDef(
+        rev="json-c-0.16-20220414",
+        build_type="cmake",
+    ),
     # Snapshot from 2019-05-24
     "linux-test-project/lcov": PackageDef(
         rev="v1.15",