End support for Python 3.7 (#299)

Python 3.8 was put at the end of life on 2023-06-27 [1], so we should
also stop supporting this version.

[1] https://devguide.python.org/versions/

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
+                python-version: ['3.8', '3.9', '3.10', '3.11', '3.12']
 
         steps:
             - name: Check out repository

pyproject.toml

@@ -16,7 +16,7 @@ classifiers = [
     "License :: OSI Approved :: MIT License",
     "Programming Language :: Python :: 3",
 ]
-requires-python = ">=3.7"
+requires-python = ">=3.8"
 dependencies = [
     "matplotlib",
     "numpy",