ci: Run test builds on min requirement PY38

Since version pinned in pyproject.toml is 38 & we've been running on 39,
we've pushed a few incompatible changes since :crie:

.github/workflows/patch-mariadb-tests.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v4
         with:
-          python-version: '3.9'
+          python-version: '3.8'
 
       - name: Setup Node
         uses: actions/setup-node@v3

.github/workflows/publish-assets-develop.yml

@@ -18,7 +18,7 @@ jobs:
           node-version: 14
       - uses: actions/setup-python@v4
         with:
-          python-version: '3.9'
+          python-version: '3.8'
       - name: Set up bench and build assets
         run: |
           npm install -g yarn

.github/workflows/publish-assets-releases.yml

@@ -21,7 +21,7 @@ jobs:
           python-version: '12.x'
       - uses: actions/setup-python@v4
         with:
-          python-version: '3.9'
+          python-version: '3.8'
       - name: Set up bench and build assets
         run: |
           npm install -g yarn

.github/workflows/server-mariadb-tests.yml

@@ -42,7 +42,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v4
         with:
-          python-version: '3.9'
+          python-version: '3.8'
 
       - name: Check if build should be run
         id: check-build

.github/workflows/server-postgres-tests.yml

@@ -45,7 +45,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v4
         with:
-          python-version: '3.9'
+          python-version: '3.8'
 
       - name: Check if build should be run
         id: check-build

.github/workflows/ui-tests.yml

@@ -41,7 +41,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v4
         with:
-          python-version: '3.9'
+          python-version: '3.8'
 
       - name: Check if build should be run
         id: check-build

frappe/utils/boilerplate.py

@@ -478,7 +478,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v2
         with:
-          python-version: 3.9
+          python-version: 3.8
 
       - name: Setup Node
         uses: actions/setup-node@v2