test: update plugins tests to use importlib.metadata directly

importlib.metadata.EntryPoint *shouldn't* differ from Python 3.8 onward,
unless there's something missing from the documentation. If this breaks
stuff on older Python releases (I'm on 3.10 locally), we will defer this
change until we drop 3.9 as planned per the code comments.

test/plugins/test_plugins_handlers.py

@@ -1,11 +1,10 @@
 """Tests for the ``sopel.plugins.handlers`` module."""
 from __future__ import annotations
 
+import importlib.metadata
 import os
 import sys
 
-# TODO: use stdlib importlib.metadata when dropping py3.9
-import importlib_metadata
 import pytest
 
 from sopel.plugins import handlers
@@ -89,7 +88,7 @@ def test_get_label_entrypoint(plugin_tmpfile):
 
     # load the entry point
     try:
-        entry_point = importlib_metadata.EntryPoint(
+        entry_point = importlib.metadata.EntryPoint(
             'test_plugin', 'file_mod', 'sopel.plugins')
         plugin = handlers.EntryPointPlugin(entry_point)
         plugin.load()

test/test_plugins.py

@@ -1,10 +1,9 @@
 """Test for the ``sopel.plugins`` module."""
 from __future__ import annotations
 
+import importlib.metadata
 import sys
 
-# TODO: switch to stdlib importlib.metdata when dropping py3.9
-import importlib_metadata
 import pytest
 
 from sopel import plugins
@@ -138,7 +137,7 @@ def test_plugin_load_entry_point(tmpdir):
 
     # load the entry point
     try:
-        entry_point = importlib_metadata.EntryPoint(
+        entry_point = importlib.metadata.EntryPoint(
             'test_plugin', 'file_mod', 'sopel.plugins')
         plugin = plugins.handlers.EntryPointPlugin(entry_point)
         plugin.load()