enh(solvers): do not allocate copt license during solver check

* COPT update

* remove empty check

* update release notes

---------

Co-authored-by: Jonas Hoersch <jonas.hoersch@openenergytransition.org>

Author: PeterKlein11

doc/release_notes.rst

@@ -5,6 +5,7 @@ Upcoming Version
 ----------------
 
 * Added support for arithmetic operations with custom classes.
+* Avoid allocating a floating license for COPT during the initial solver check
 
 Version 0.5.0
 --------------

linopy/solvers.py

@@ -111,10 +111,7 @@
 with contextlib.suppress(ModuleNotFoundError):
     import coptpy
 
-    with contextlib.suppress(coptpy.CoptError):
-        coptpy.Envr()
-
-        available_solvers.append("copt")
+    available_solvers.append("copt")
 
 quadratic_solvers = [s for s in QUADRATIC_SOLVERS if s in available_solvers]
 logger = logging.getLogger(__name__)