Update SymPy Dependency + Pipeline Cleanup

This MR

• raises the upper limit for SymPy to 1.12.1
• introduces a weekly test run against the latest sympy pre-release
• cleans up the CI configuration a bit

Closes #91 (closed)

.gitlab-ci.yml

@@ -3,6 +3,7 @@ stages:
   - test
   - nightly
   - docs
+  - deploy
 
 
 # --------------------------  Templates ------------------------------------------------------------------------------------
@@ -296,7 +297,7 @@ build-documentation:
 pages:
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/full
   # extends: .every-commit
-  stage: docs
+  stage: deploy
   needs: ["build-documentation"]
   script:
     - ls -l