Install problemtools from master branch

This avoids them setting a fixed, but old Kotlin version in the default develop branch.

Author: stoman

.github/workflows/verify-problems.yml

@@ -13,13 +13,11 @@ jobs:
         uses: actions/setup-python@v5
         with:
           python-version: '3.x'
-      - name: Set up Kotlin
-        uses: fwilhe2/setup-kotlin@main
       - name: Install dependencies
         run: |
           sudo apt install automake g++ make libboost-regex-dev libgmp-dev libgmp10 libgmpxx4ldbl python3 python3-pytest python3-setuptools python3-yaml python3-plastex python3-unidecode
           python -m pip install --upgrade pip
-          pip install git+https://github.com/kattis/problemtools
+          pip install git+https://github.com/kattis/problemtools@master
           pip install -r requirements.txt
           python3 problems/statistics10multiplelinearregression/submissions/accepted/stefan.py < problems/statistics10multiplelinearregression/data/sample/1.in
       - name: Verify problems