tests: workers=1 since some pytest+multiprocessing problem

tests/test_solver.py

@@ -101,7 +101,7 @@ def test_example_sss_1d_J_usadel1():
 
     T_c0 = np.exp(np.euler_gamma) / np.pi
     T = 0.2
-    Delta, I0, _, success = sol.self_consistency(T=T, T_c0=T_c0, workers=-1)
+    Delta, I0, _, success = sol.self_consistency(T=T, T_c0=T_c0, workers=1)
 
     tau3 = np.diag([1, 1, -1, -1])
     I0 = tr(I0[:-1, 0, 0] @ tau3)
@@ -221,7 +221,7 @@ def test_selfcons_kupriyanov(request, T):
         T_c0=Tc0,
         phase_mask=phase_mask,
         filename=cache_fn,
-        workers=-1,
+        workers=1,
         ds=0.4,
     )