Remove pytest-subtests and migrate to new TOML config format

Co-authored-by: jb3 <[email protected]>

Author: Copilot

pyproject.toml

@@ -40,7 +40,6 @@ dev = [
     "pre-commit==4.3.0",
     "pytest==9.0.0",
     "pytest-cov==7.0.0",
-    "pytest-subtests==0.14.1",
     "pytest-xdist==3.8.0",
     "ruff==0.14.2",
     "taskipy==1.14.1",
@@ -96,8 +95,8 @@ combine-as-imports = true
 [tool.ruff.lint.per-file-ignores]
 "tests/*" = ["ANN", "D"]
 
-[tool.pytest.ini_options]
+[tool.pytest]
 # We don't use nose style tests so disable them in pytest.
 # This stops pytest from running functions named `setup` in test files.
 # See https://github.com/python-discord/bot/pull/2229#issuecomment-1204436420
-addopts = "-p no:nose"
+addopts = ["-p", "no:nose"]