Fix test isolation bug in test_startup_error_from_plugin_is_click_exception (#2627)

* Fix test isolation bug in test_startup_error_from_plugin_is_click_exception

The test creates a plugin that raises StartupError("boom") and registers it
in the global plugin manager (pm). Without cleanup, this plugin leaks to
subsequent tests, causing test_setting_boolean_validation_false_values to
fail with "Error: boom" instead of "Forbidden".

Add try/finally block to ensure the plugin is unregistered after the test
completes, following the established cleanup pattern used elsewhere in
the test suite.

* Fix blacken-docs formatting in plugin_hooks.rst

Apply blacken-docs formatting to code example that exceeded
the 60 character line limit.

---------

Co-authored-by: Claude <noreply@anthropic.com>

docs/plugin_hooks.rst

@@ -967,11 +967,14 @@ Here is an example that validates required plugin configuration. The server will
 
     from datasette.utils import StartupError
 
+
     @hookimpl
     def startup(datasette):
         config = datasette.plugin_config("my-plugin") or {}
         if "required-setting" not in config:
-            raise StartupError("my-plugin requires setting required-setting")
+            raise StartupError(
+                "my-plugin requires setting required-setting"
+            )
 
 You can also return an async function, which will be awaited on startup. Use this option if you need to execute any database queries, for example this function which creates the ``my_table`` database table if it does not yet exist:
 

tests/test_cli.py

@@ -4,7 +4,7 @@ from .fixtures import (
     EXPECTED_PLUGINS,
 )
 from datasette.app import SETTINGS
-from datasette.plugins import DEFAULT_PLUGINS
+from datasette.plugins import DEFAULT_PLUGINS, pm
 from datasette.cli import cli, serve
 from datasette.version import __version__
 from datasette.utils import tilde_encode
@@ -326,8 +326,16 @@ def test_startup_error_from_plugin_is_click_exception(tmp_path):
             "/",
         ],
     )
-    assert result.exit_code == 1
-    assert "Error: boom" in result.output
+    try:
+        assert result.exit_code == 1
+        assert "Error: boom" in result.output
+    finally:
+        # Cleanup: Unregister the plugin to avoid test isolation issues
+        to_unregister = [
+            p for p in pm.get_plugins() if p.__name__ == "startup_error.py"
+        ]
+        if to_unregister:
+            pm.unregister(to_unregister[0])
 
 
 def test_setting_type_validation():