ci: Pin pip v25.3 until pip-tools is compatible

pip v26.0 came out and is installed on windows-latest. pip-tools v7.5.2 is not compatible yet.
Wait until jazzband/pip-tools#2320 is released

Author: alessiamarcolini

.github/workflows/update_env.yml

@@ -24,6 +24,7 @@ jobs:
         python-version: "3.11"
     - name: Compile
       run: |
+        python -m pip install pip==25.3
         python -m pip install pip-tools==7.5.2
         python .github/workflows/update_env.py compile
     - uses: actions/upload-artifact@v4