Improve checks in CI/CD

Currently we just lint, but we would benefit from doing what I have in my pre-commit script:
```bash
set -e

# check typescript correctness
npx tsc --noEmit

# check all .sh files are executable
invalid_scripts=0
for script in $( find . -type f -iname *.sh ); do
if [ ! -x $script ]; then
echo "Script $script is not executable"
invalid_scripts=$((invalid_scripts + 1))
fi
done
if [ $invalid_scripts != 0 ]; then
exit 1
fi

# check there are no it.only occurrences in the tests
grep -re "it\.only(" $(git ls-files '*.ts') && echo "Error: There are files with it.only(...)" && exit 2

# lint
npm run lint
```

Look for the CI/CD configuration file (likely .github/workflows/*.yml) to understand the current linting step. The issue provides a bash script to integrate: it runs TypeScript type checking, ensures .sh files are executable, checks for stray it.only in test files, and then runs linting. Start by locating where the CI script runs and add these checks in the appropriate order. Verify by running the script locally and then updating the CI configuration.

Vom Indexierungsmodell aus dem Issue-Text verfasst.