Fix CITATION.cff (#887)

* Remove `version` and `date-released` attributes which mess up Zenodo metadata if not updated on every release
* Add required `message`
* Auto-validate via GHA

.github/workflows/ci.yml

@@ -206,6 +206,9 @@ jobs:
     - name: Install dependencies
       run: .github/workflows/install_deps.sh doc amici
 
+    - name: Validate CITATION.cff
+      run: pip install cffconvert && cffconvert --validate
+
     - name: Build doc
       timeout-minutes: 5
       run: tox -e doc

CITATION.cff

@@ -1,3 +1,4 @@
+message: If you use this software, please cite it using these metadata.
 authors:
    -
       family-names: "Schälte"
@@ -70,6 +71,4 @@ authors:
 title: "pyPESTO - Parameter EStimation TOolbox for python"
 url: "https://github.com/ICB-DCM/pyPESTO"
 doi: 10.5281/zenodo.2553546
-version: 0.2.7
-date-released: 2021-03-08
 cff-version: 1.2.0