Extensions Added Twice When Custom Directives Are Present

[doney-dkp]

Describe the Bug
When custom directives are added, extensions are appended twice in the get_extensions function in the schema.py file.

Issue
In the following code:
https://github.com/strawberry-graphql/strawberry/blob/main/strawberry/schema/schema.py
line 299

    def get_extensions(self, sync: bool = False) -> list[SchemaExtension]:
        extensions = []
        if self.directives:
            extensions = [
                *self.extensions,
                DirectivesExtensionSync if sync else DirectivesExtension,
            ]
        extensions.extend(self.extensions)
        return [
            ext if isinstance(ext, SchemaExtension) else ext(execution_context=None)
            for ext in extensions
        ]

The extensions list already contains self.extensions, and then extend(self.extensions) adds them again, causing duplicates.

Example Reproduction

>>> ex = ["a", "b"]
>>> extensions = [*ex]
>>> extensions
['a', 'b']
>>> extensions.extend(ex)
>>> extensions
['a', 'b', 'a', 'b']

Expected Behavior
Extensions should not be duplicated when custom directives are present.

Suggested Fix
Modify the logic to avoid adding self.extensions twice.
remove line extensions.extend(self.extensions)

[bellini666]

Hey @doney-dkp ,

nice catch there!

Do you want to try to submit a PR to fix that?

[doney-dkp]

@bellini666 sure, happy to do