MAINT: drop Python 3.7 & 3.8 support due to EOL (#9)

* MAINT: modernize Python syntax to Python 3.9

pyproject.toml

@@ -16,8 +16,6 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
-    "Programming Language :: Python :: 3.7",
-    "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python",
     "Topic :: Documentation",
@@ -35,7 +33,7 @@ keywords = [
 license = {text = "BSD 3-Clause License"}
 maintainers = [{email = "[email protected]"}]
 name = "sphinx-pybtex-etal-style"
-requires-python = ">=3.7"
+requires-python = ">=3.9"
 
 [project.optional-dependencies]
 dev = ["sphinx-pybtex-etal-style[sty]"]
@@ -127,7 +125,7 @@ typeCheckingMode = "strict"
 preview = true
 show-fixes = true
 src = ["src"]
-target-version = "py37"
+target-version = "py39"
 
 [tool.ruff.format]
 docstring-code-format = true

src/sphinx_pybtex_etal_style/style.py

@@ -3,8 +3,7 @@
 # pyright: reportMissingTypeStubs=false
 from __future__ import annotations
 
-import sys
-from typing import TYPE_CHECKING, ClassVar
+from typing import TYPE_CHECKING, ClassVar, Literal
 
 from pybtex.richtext import Tag, Text
 from pybtex.style.formatting.unsrt import Style as UnsrtStyle
@@ -22,10 +21,6 @@
 
 if TYPE_CHECKING:
     from pybtex.database import Entry
-if sys.version_info < (3, 8):
-    from typing_extensions import Literal
-else:
-    from typing import Literal
 
 
 ISBNResolvers = Literal["bookfinder", "isbnsearch"]