build-unit-test-docker: cereal: get upstream c++20 fixes

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Iaa03418fdad4405f2f102c283bfaafcdad10c042
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index bcc337d..b1c4567 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -90,7 +90,7 @@
         ],
     ),
     "USCiLab/cereal": PackageDef(
-        rev="v1.3.0",
+        rev="3e4d1b84cab4891368d2179a61a7ba06a5693e7f",
         build_type="custom",
         build_steps=[f"cp -a include/cereal/ {prefix}/include/"],
     ),