Use ShapeID instead of string literal

[jonathan343]

Fixes the following type checking errors when trying to build the aws_sdk_bedrock_runtime client:

Projection client failed: software.amazon.smithy.codegen.core.CodegenException: Command `python3 -m pyright .` failed with output:

/Users/gytndd/dev/new-bedrock/build/smithy/client/python-client-codegen/src/aws_sdk_bedrock_runtime/auth.py
  /Users/gytndd/dev/new-bedrock/build/smithy/client/python-client-codegen/src/aws_sdk_bedrock_runtime/auth.py:25:19 - error: Argument of type "Literal['aws.auth#sigv4']" cannot be assigned to parameter "scheme_id" of type "ShapeID" in function "__init__"
    "Literal['aws.auth#sigv4']" is not assignable to "ShapeID" (reportArgumentType)
1 error, 0 warnings, 0 informations 
WARNING: there is a new pyright version available (v1.1.400 -> v1.1.403).
Please install the new version or set PYRIGHT_PYTHON_FORCE_VERSION to `latest`

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