Fix mypy errors in pytorch_lightning/strategies/sharded.py

[lijm1358]

What does this PR do?

Fixes mypy typing errors in pytorch_lightning/strategies/sharded.py in #13445

src/pytorch_lightning/strategies/sharded.py:55: error: Cannot determine type of "_rank_0_will_call_children_scripts"  [has-type]
src/pytorch_lightning/strategies/sharded.py:59: error: Item "None" of "Optional[Accelerator]" has no attribute "setup"  [union-attr]
src/pytorch_lightning/strategies/sharded.py:68: error: Argument 1 to "apply" of "LayerSync" has incompatible type "Optional[Module]"; expected Module  [arg-type]
src/pytorch_lightning/strategies/sharded.py:77: error: Item "None" of "Optional[Module]" has no attribute "trainer"  [union-attr]
src/pytorch_lightning/strategies/sharded.py:77: error: Argument 1 to "setup_optimizers" of "Strategy" has incompatible type "Union[Tensor, Module, Any]"; expected "Trainer"  [arg-type]
src/pytorch_lightning/strategies/sharded.py:79: error: Argument 1 to "_LightningModuleWrapperBase" has incompatible type "Optional[Module]"; expected "Union[LightningModule, _LightningPrecisionModuleWrapperBase, None]"  [arg-type]
src/pytorch_lightning/strategies/sharded.py:101: error: Item "Tensor" of "Union[Tensor, Module]" has no attribute "state"  [union-attr]
src/pytorch_lightning/strategies/sharded.py:101: error: Item "Tensor" of "Union[Any, Tensor, Module]" has no attribute "fn"  [union-attr]
src/pytorch_lightning/strategies/sharded.py:104: error: Argument 1 to "_reinit_optimizers_with_oss" of "DDPShardedStrategy" has incompatible type "List[Optimizer]"; expected "List[Union[Optimizer, LightningOptimizer]]"  [arg-type]
src/pytorch_lightning/strategies/sharded.py:104: note: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
src/pytorch_lightning/strategies/sharded.py:104: note: Consider using "Sequence" instead, which is covariant
src/pytorch_lightning/strategies/sharded.py:123: error: Return type "Optional[Dict[Any, Any]]" of "optimizer_state" incompatible with return type "Dict[str, Tensor]" in supertype "Strategy"  [override]
src/pytorch_lightning/strategies/sharded.py:130: error: Function is missing a type annotation  [no-untyped-def]
src/pytorch_lightning/strategies/sharded.py:153: error: Function is missing a return type annotation  [no-untyped-def]
src/pytorch_lightning/strategies/sharded.py:153: note: Use "-> None" if function does not return a value
Found 12 errors in 1 file (checked 223 source files)

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[awaelchli]

Thx!!