chore: drop long-unsupported Python 3.7

Python 3.7 hasn't been supported in ages, and it's causing errors on CI actions.
Let's just drop it.

.github/workflows/ci.yml

@@ -15,7 +15,6 @@ jobs:
         uses: fabiocaccamo/create-matrix-action@v3
         with:
           matrix: |
-            python-version {3.7}, django-version {2.0,2.1,2.2,3.0,3.1}
             python-version {3.8}, django-version {2.2,3.0,3.1,3.2,4.0,4.1,4.2}
             python-version {3.9}, django-version {2.2,3.0,3.1,3.2,4.0,4.1,4.2}
             python-version {3.10}, django-version {3.2,4.0,4.1,4.2,5.0,5.1}

pyproject.toml

@@ -20,7 +20,6 @@ classifiers = [
   "License :: OSI Approved :: Apache Software License",
   "Operating System :: OS Independent",
   "Programming Language :: Python :: 3",
-  "Programming Language :: Python :: 3.7",
   "Programming Language :: Python :: 3.8",
   "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
@@ -29,7 +28,7 @@ classifiers = [
 ]
 
 [tool.poetry.dependencies]
-python = "^3.7"
+python = "^3.8"
 
 [tool.poetry.group.dev.dependencies]
 coverage = "7.*"