[Bug-Candidate]: Vyper unpacking call's returned values crash Slither

[trocher]

Describe the issue:

When unpacking the returned values of a call, if multiple values are returned, Slither crashes.

Code example to reproduce the issue:

# @version 0.3.7

interface X:
    def bar() -> (address, address): nonpayable

@internal
def foo(x: X):

    a: address = empty(address)
    b: address = empty(address)
    a, b = x.bar()

Version:

0.10.1

Relevant log output:

Traceback (most recent call last):
  File "/home/csdocker/.local/bin/slither", line 8, in <module>
    sys.exit(main())
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/__main__.py", line 746, in main
    main_impl(all_detector_classes=detectors, all_printer_classes=printers)
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/__main__.py", line 852, in main_impl
    ) = process_all(filename, args, detector_classes, printer_classes)
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/__main__.py", line 107, in process_all
    ) = process_single(compilation, args, detector_classes, printer_classes)
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/__main__.py", line 80, in process_single
    slither = Slither(target, ast_format=ast, **vars(args))
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/slither.py", line 150, in __init__
    self._init_parsing_and_analyses(kwargs.get("skip_analyze", False))
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/slither.py", line 170, in _init_parsing_and_analyses
    raise e
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/slither.py", line 166, in _init_parsing_and_analyses
    parser.analyze_contracts()
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/vyper_parsing/vyper_compilation_unit.py", line 63, in analyze_contracts
    self._convert_to_slithir()
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/vyper_parsing/vyper_compilation_unit.py", line 73, in _convert_to_slithir
    func.generate_slithir_and_analyze()
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/core/declarations/function.py", line 1772, in generate_slithir_and_analyze
    node.slithir_generation()
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/core/cfg/node.py", line 717, in slithir_generation
    self._irs = convert_expression(expression, self)  # type:ignore
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/slithir/convert.py", line 115, in convert_expression
    visitor = ExpressionToSlithIR(expression, node)
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/visitors/slithir/expression_to_slithir.py", line 174, in __init__
    self._visit_expression(self.expression)
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/visitors/expression/expression.py", line 93, in _visit_expression
    self._post_visit(expression)
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/visitors/expression/expression.py", line 267, in _post_visit
    self._post_assignement_operation(expression)
  File "/home/csdocker/.local/share/pipx/venvs/slither-analyzer/lib/python3.10/site-packages/slither/visitors/slithir/expression_to_slithir.py", line 209, in _post_assignement_operation
    assert isinstance(right, TupleVariable)
AssertionError