test: add JuliaSimCompiler only to run its integration tests

Remove `JuliaSimCompiler` as a test dependency as that would require
having access to the package at all times to run the tests, making it
synonymous with a direct dependency (and less of an extension) in the
context of running tests.
Instead, explicitly `Pkg.add` `JuliaSimCompiler` instead in the
relevant test matrices.

Project.toml

@@ -48,11 +48,11 @@ TermInterface = "0.2, 0.3"
 julia = "1.6"
 
 [extras]
-JuliaSimCompiler = "8391cb6b-4921-5777-4e45-fd9aab8cb88d"
 NonlinearSolve = "8913a72c-1f9b-4ce2-8d82-65094dcecaec"
+Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
 SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
 StableRNGs = "860ef19b-820b-49d6-a774-d7a799459cd3"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Test", "NonlinearSolve", "SafeTestsets", "StableRNGs", "JuliaSimCompiler"]
+test = ["Test", "NonlinearSolve", "SafeTestsets", "StableRNGs", "Pkg"]

test/runtests.jl

@@ -1,4 +1,5 @@
 using SafeTestsets
+using Pkg
 
 const GROUP = get(ENV, "GROUP", "All")
 const is_APPVEYOR = Sys.iswindows() && haskey(ENV, "APPVEYOR")
@@ -129,11 +130,13 @@ const is_TRAVIS = haskey(ENV, "TRAVIS")
     end
     ############### JSC #####################
     if GROUP == "All" || GROUP == "MOL_Interface2_JSC"
+        Pkg.add("JuliaSimCompiler")
         @time @safetestset "MOLFiniteDifference Interface" begin
             include("pde_systems/MOLtest2_JSC.jl")
         end
     end
     if GROUP == "All" || GROUP == "MOL_Interface1_JSC"
+        Pkg.add("JuliaSimCompiler")
         @time @safetestset "MOLFiniteDifference Interface" begin
             include("pde_systems/MOLtest1_JSC.jl")
         end