Update GitHub Actions Python version

.github/workflows/master_linkcheck.yml

@@ -15,10 +15,10 @@ jobs:
     name: Check for broken links
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.7
+    - name: Set up Python 3.8
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.8
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip

.github/workflows/master_warnings.yml

@@ -12,10 +12,10 @@ jobs:
     name: Check for warnings
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.7
+    - name: Set up Python 3.8
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.8
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip

.github/workflows/pr_build.yml

@@ -11,10 +11,10 @@ jobs:
     name: Build to check for warnings
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.7
+    - name: Set up Python 3.8
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.8
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip

.github/workflows/update_translation_files.yml

@@ -16,10 +16,10 @@ jobs:
     name: Update translation files
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.7
+    - name: Set up Python 3.8
       uses: actions/setup-python@v2
       with:
-        python-version: 3.7
+        python-version: 3.8
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip