CI: Update diffrax branch (AMICI-dev#3123)

`dev` is gone:
https://github.com/patrick-kidger/diffrax/branches/all?query=dev

Author: dweindl

.github/workflows/test_benchmark_collection_models.yml

@@ -132,7 +132,7 @@ jobs:
         &&  python3 -m pip install -U sympy \
         &&  python3 -m pip install git+https://github.com/ICB-DCM/fiddy.git@amici100
 
-    - run: pip uninstall -y diffrax && pip install git+https://github.com/patrick-kidger/diffrax@dev # TODO FIXME https://github.com/patrick-kidger/diffrax/issues/654 + event dirs
+    - run: pip uninstall -y diffrax && pip install git+https://github.com/patrick-kidger/diffrax@main # TODO FIXME https://github.com/patrick-kidger/diffrax/issues/654 + event dirs
 
     - name: Download benchmark collection
       run: |

scripts/installAmiciSource.sh

@@ -38,7 +38,7 @@ python -m pip install --upgrade pip wheel
 #  The latter is necessary for code coverage to work.
 python -m pip install --upgrade pip setuptools cmake_build_extension==0.6.0 numpy petab swig
 python -m pip install git+https://github.com/pysb/pysb@master # for SPM with compartments
-python -m pip install git+https://github.com/patrick-kidger/diffrax@dev # for events with direction
+python -m pip install git+https://github.com/patrick-kidger/diffrax@main # for events with direction
 python -m pip install optax # for jax petab notebook
 AMICI_BUILD_TEMP="${AMICI_PATH}/python/sdist/build/temp" \
   python -m pip install --verbose -e "${AMICI_PATH}/python/sdist[petab,test,vis,jax]" --no-build-isolation