test: add MSL to downstream env

Author: DhairyaLGandhi

test/downstream/Project.toml

@@ -3,6 +3,7 @@ BoundaryValueDiffEq = "764a87c0-6b3e-53db-9096-fe964310641d"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 JumpProcesses = "ccbc3e58-028d-4f4c-8cd5-9ae44345cda5"
 ModelingToolkit = "961ee093-0014-501f-94e3-6117800e7a78"
+ModelingToolkitStandardLibrary = "16a59e39-deab-5bd0-87e4-056b12336739"
 NonlinearSolve = "8913a72c-1f9b-4ce2-8d82-65094dcecaec"
 Optimization = "7f7a1694-90dd-40f0-9382-eb1efda571ba"
 OptimizationMOI = "fd9f6733-72f4-499f-8506-86b2bdd0dea1"
@@ -22,6 +23,7 @@ BoundaryValueDiffEq = "5"
 ForwardDiff = "0.10"
 JumpProcesses = "9.10"
 ModelingToolkit = "8.37, 9"
+ModelingToolkitStandardLibrary = "2.7"
 NonlinearSolve = "2, 3"
 Optimization = "3"
 OptimizationMOI = "0.4"