[core] Move pytest config into pyproject.toml (#6740)

pyproject.toml

@@ -54,3 +54,12 @@ include = ["esphome*"]
 [tool.black]
 target-version = ["py39", "py310"]
 exclude = 'generated'
+
+[tool.pytest.ini_options]
+testpaths = [
+  "tests",
+]
+addopts = [
+  "--cov=esphome",
+  "--cov-branch",
+]

pytest.ini

@@ -1,4 +0,0 @@
-[pytest]
-addopts =
-    --cov=esphome
-    --cov-branch