Drop support for python 3.8.

Update metadata in `pyproject.toml` to reflect that python 3.8 is no longer
supported. This is due to recent addition of `pre-commit` as a dependency.

Author: glenn20

pyproject.toml

@@ -7,10 +7,8 @@ urls = {Homepage = "https://github.com/glenn20/mp-image-tool-esp32"}
 license = {text = "MIT"}
 classifiers = [
     "License :: OSI Approved :: MIT License",
-    "Programming Language :: Python :: 3",
     "Operating System :: OS Independent",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",