Fix: Only enforce content length for GET requests

[rcoh]

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[github-actions]

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• AWS SDK (ignoring whitespace)
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• No codegen difference in the Server Test Python
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[ysaito1001]

Thanks Russell. We just need to change the target branch to main for this PR, instead of the release branch. We discovered a couple of weeks ago that directly bumping a runtime crate in the release branch without cutting a release confused runtime-versioner audit

runtime versioner refers to the latest release in smithy-rs when detecting baseline crates versions and compares those in the current active branch. If a runtime crate version gets bumped "secretly" in the release branch without a new release tag and subsequently published to crates.io, then the tool gets confused and complains that the crate version is ahead of the latest release tag but somehow that version is already available on crates.io.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.