Update HiGHS test configuration in CI workflow

Removed parallel test execution for HiGHS package to avoid errors.

Author: odow

.github/workflows/julia-tests.yml

@@ -115,12 +115,7 @@ jobs:
       - shell: julia --color=yes {0}
         run: |
           using Pkg
-          # HiGHS uses (N+1)/2 threads. HiGHS.jl parallelises the tests and, in
-          # the default setting, it may use up to 4 parallel jobs. This means
-          # HiGHS may attempt to start up to 2(N+1) threads and we get unhandled
-          # exceptions on macOS and a SIGTERM on linux. To avoid these errors,
-          # opt out of running the tests in parallel.
-          Pkg.test("HiGHS"; test_args=["--parallel=false"])
+          Pkg.test("HiGHS")
       # An attempt to reproduce
       # https://github.com/jump-dev/MultiObjectiveAlgorithms.jl/pull/211
       - shell: julia --color=yes {0}