Drop support for 3.8, which is near EOL.

And some other minor tweaks to the pyproject.toml which match
what we use in other JSON Schema projects.

pyproject.toml

@@ -8,9 +8,8 @@ source = "vcs"
 [project]
 name = "jsonschema-specifications"
 description = "The JSON Schema meta-schemas and vocabularies, exposed as a Registry"
+requires-python = ">=3.9"
 readme = "README.rst"
-license = {text = "MIT"}
-requires-python = ">=3.8"
 keywords = [
     "validation",
     "data validation",
@@ -35,12 +34,12 @@ classifiers = [
   "Programming Language :: Python :: 3.13",
   "Programming Language :: Python :: Implementation :: CPython",
   "Programming Language :: Python :: Implementation :: PyPy",
+  "Topic :: File Formats :: JSON",
   "Topic :: File Formats :: JSON :: JSON Schema",
 ]
 dynamic = ["version"]
 dependencies = [
   "referencing>=0.31.0",
-  "importlib_resources>=1.4.0;python_version<'3.9'",
 ]
 
 [project.urls]
@@ -75,13 +74,6 @@ ignore = [
     "D001",  # one sentence per line, so max length doesn't make sense
 ]
 
-[tool.isort]
-combine_as_imports = true
-ensure_newline_before_comments = true
-from_first = true
-include_trailing_comma = true
-multi_line_output = 3
-
 [tool.ruff]
 line-length = 79
 
@@ -109,7 +101,7 @@ ignore = [
   "D406",  # Section headers should end with a colon not a newline
   "D407",  # Underlines aren't needed
   "D412",  # Plz spaces after section headers
-  "EM101",  # These don't bother me.
+  "EM101",  # These don't bother me, it's fine there's some duplication.
   "EM102",
   "FBT",  # It's worth avoiding boolean args but I don't care to enforce it
   "FIX",  # Yes thanks, if I could it wouldn't be there
@@ -119,7 +111,9 @@ ignore = [
   "PLR0915",
   "PLW2901",  # Shadowing for loop variables is occasionally fine.
   "PT006",  # pytest parametrize takes strings as well
-  "RET503",  # Returning None implicitly is fine
+  "PYI025",  # wat, I'm not confused, thanks.
+  "RET502",  # Returning None implicitly is fine
+  "RET503",
   "RET505",  # These push you to use `if` instead of `elif`, but for no reason
   "RET506",
   "RSE102",  # Ha, what, who even knew you could leave the parens off. But no.