fix: add mindopt license check (#393)

Author: lkstrp

linopy/solvers.py

@@ -103,7 +103,10 @@
 with contextlib.suppress(ModuleNotFoundError):
     import mindoptpy
 
-    available_solvers.append("mindopt")
+    with contextlib.suppress(mindoptpy.MindoptError):
+        mindoptpy.Env()
+
+        available_solvers.append("mindopt")
 
 with contextlib.suppress(ModuleNotFoundError):
     import coptpy