Only install Felis rather than using separate requirements

Install Felis rather than using a separate requirements.txt file, as
this may contain conflicting depedency versions.

.github/workflows/build.yaml

@@ -20,8 +20,12 @@ jobs:
           cache: "pip"
 
       - name: Install dependencies
-        id: depend
-        run: pip install -r requirements.txt
+        # Only install Felis rather than using the separate requirements.txt,
+        # since the dependencies may conflict. Felis already includes all the
+        # required dependencies for the tap-schema build.
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install git+http://github.com/lsst/felis.git@main#egg=felis
         working-directory: ./tap-schema
 
       - name: Log in to Docker Hub