Add stubs for flake8-bugbear (#6543)

stubs/flake8-bugbear/@tests/stubtest_allowlist.txt

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+bugbear.BugBearChecker.__getattr__

stubs/flake8-bugbear/METADATA.toml

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+version = "21.11.29"

stubs/flake8-bugbear/bugbear.pyi

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+import argparse
+import ast
+from typing import Any, Sequence
+
+class BugBearChecker:
+    name: str
+    version: str
+    tree: ast.AST | None
+    filename: str
+    lines: Sequence[str] | None
+    max_line_length: int
+    visitor: ast.NodeVisitor
+    options: argparse.Namespace | None
+    def run(self) -> None: ...
+    @staticmethod
+    def add_options(optmanager: Any) -> None: ...
+    def __init__(
+        self,
+        tree: ast.AST | None = ...,
+        filename: str = ...,
+        lines: Sequence[str] | None = ...,
+        max_line_length: int = ...,
+        options: argparse.Namespace | None = ...,
+    ) -> None: ...
+    def __getattr__(self, name: str) -> Any: ...  # incomplete (other attributes are normally not accessed)
+
+def __getattr__(name: str) -> Any: ...  # incomplete (other attributes are normally not accessed)