CI: don't cache amici; pytest ignore amici_models; passenv BNGPATH

* Don't cache the amici installation.
  We are using amici/develop on purpose to detect problems early on. E.g., #1520 should have been detected much earlier.
* Ignore `amici_models` when collecting tests
* Use external BNGPATH if set

.github/workflows/ci.yml

@@ -157,7 +157,7 @@ jobs:
 
     - name: Run tests
       timeout-minutes: 35
-      run: tox -e petab
+      run: tox -e petab && tox e -e petab -- pip uninstall -y amici
       env:
         CC: clang
         CXX: clang++

pytest.ini

@@ -2,3 +2,4 @@
 addopts = "--doctest-modules"
 filterwarnings =
     ignore:.*inspect.getargspec\(\) is deprecated.*:DeprecationWarning
+norecursedirs = amici_models

tox.ini

@@ -29,7 +29,7 @@ envlist =
 # Base-environment
 
 [testenv]
-passenv = AMICI_PARALLEL_COMPILE,CC,CXX,MPLBACKEND
+passenv = AMICI_PARALLEL_COMPILE,CC,CXX,MPLBACKEND,BNGPATH
 
 # Sub-environments
 #  inherit settings defined in the base