Install python 3.8, not 3.7, in ci

3.8 is what we use for tests workflow, and more importantly the
pyproject.toml spec says `python = "^3.8"`

Author: lacop11

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
       - name: Set up python
         uses: actions/setup-python@v4
         with:
-          python-version: 3.7
+          python-version: 3.8
       - name: Bootstrap poetry
         run: |
           curl -sSL https://install.python-poetry.org | python - -y --version 1.5.1
@@ -26,7 +26,7 @@ jobs:
       - name: Set up python
         uses: actions/setup-python@v4
         with:
-          python-version: 3.7
+          python-version: 3.8
       - name: Bootstrap poetry
         run: |
           curl -sSL https://install.python-poetry.org | python - -y --version 1.5.1
@@ -48,7 +48,7 @@ jobs:
       - name: Set up python
         uses: actions/setup-python@v4
         with:
-          python-version: 3.7
+          python-version: 3.8
       - name: Bootstrap poetry
         run: |
           curl -sSL https://install.python-poetry.org | python - -y --version 1.5.1