Upgrade default python to 3.9 in build.yaml (#855)

Signed-off-by: Fabrice Normandin <fabrice.normandin@gmail.com>

.github/workflows/build.yml

@@ -21,10 +21,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v1
-    - name: Set up Python 3.7
+    - name: Set up Python 3.9
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.9
     - name: Install dependencies
       run: |
           python -m pip install --upgrade pip
@@ -66,10 +66,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v1
-    - name: Set up Python 3.7
+    - name: Set up Python 3.9
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.9
     - name: Install dependencies
       run: |
           python -m pip install --upgrade pip
@@ -89,10 +89,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v1
-      - name: Set up Python 3.7
+      - name: Set up Python 3.9
         uses: actions/setup-python@v2
         with:
-          python-version: 3.7
+          python-version: 3.9
       - name: Setup MongoDB
         uses: supercharge/mongodb-github-action@1.3.0
         with:
@@ -124,10 +124,10 @@ jobs:
       ORION_DB_TYPE: ${{ matrix.orion_db_type }}
     steps:
     - uses: actions/checkout@v1
-    - name: Set up Python 3.7
+    - name: Set up Python 3.9
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.9
     - name: Setup MongoDB
       uses: supercharge/mongodb-github-action@1.3.0
       with:
@@ -153,10 +153,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v1
-    - name: Set up Python 3.7
+    - name: Set up Python 3.9
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.9
     - name: Install dependencies
       run: |
           python -m pip install --upgrade pip
@@ -185,10 +185,10 @@ jobs:
         ANACONDA_TOKEN: ${{ secrets.anaconda_token }}
     steps:
     - uses: actions/checkout@v1
-    - name: Set up Python 3.7
+    - name: Set up Python 3.9
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.9
     - name: Build conda
       run: ./conda/ci_build.sh
     - name: Publish distribution 📦 to Conda