build-unit-test-docker: add nlohmann-json dep to sdbusplus

Pending commit[1] adds nlohmann-json usage in sdbusplus;
update docker dependencies to reflect that.

[1]: https://gerrit.openbmc.org/c/openbmc/sdbusplus/+/74858

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I9027c06877c35ae9c5b130d1ce0bec881060b5d7
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index f7de137..4af1f8d 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -231,6 +231,9 @@
         ],
     ),
     "openbmc/sdbusplus": PackageDef(
+        depends=[
+            "nlohmann/json",
+        ],
         build_type="meson",
         custom_post_dl=[
             "cd tools",