Disable multiple threads for Cbc solver on Windows

Cbc cannot be used on Windows with multiple threads: <jump-dev/Cbc.jl#186>
The `threads` argument is already disabled on Windows since Cbc v1.0.0: <jump-dev/Cbc.jl#192>
We cannot use Cbc v1.0.0 at the moment because it requires MathOptInterface v1 and we require MathOptInterface v0.10.9.
Removal of MathOptInterface from FlexPlan.jl dependencies is to be done: <#121 (comment)>

test/runtests.jl

@@ -24,7 +24,17 @@ using Test
 
 ipopt_solver = JuMP.optimizer_with_attributes(Ipopt.Optimizer, "tol" => 1e-6, "print_level" => 0)
 scs_solver = JuMP.optimizer_with_attributes(SCS.Optimizer, "verbose" => 0)
-cbc = JuMP.optimizer_with_attributes(Cbc.Optimizer, "logLevel" => 0, "threads"=>Threads.nthreads())
+
+# Cbc cannot be used on Windows with multiple threads: <https://github.com/jump-dev/Cbc.jl/issues/186>
+# The `threads` argument is already disabled on Windows since Cbc v1.0.0: <https://github.com/jump-dev/Cbc.jl/pull/192>
+# We cannot use Cbc v1.0.0 at the moment because it requires MathOptInterface v1 and we require MathOptInterface v0.10.9.
+# Removal of MathOptInterface from FlexPlan.jl dependencies is to be done: <https://github.com/Electa-Git/FlexPlan.jl/issues/121#issue-1158572058>
+if Sys.iswindows()
+    cbc = JuMP.optimizer_with_attributes(Cbc.Optimizer, "logLevel" => 0)
+else
+    cbc = JuMP.optimizer_with_attributes(Cbc.Optimizer, "logLevel" => 0, "threads"=>Threads.nthreads())
+end
+
 juniper = JuMP.optimizer_with_attributes(Juniper.Optimizer, "nl_solver" => ipopt_solver, "mip_solver" => cbc, "time_limit" => 7200)
 
 @testset "FlexPlan" begin