add missing include

[sbiscigl]

Issue #, if available:

#3838

Description of changes:

adds missing include that breaks musl toolchains

replicated/verified fix with

FROM alpine:3.23

RUN apk add --no-cache build-base cmake ninja git curl-dev openssl-dev zlib-dev

RUN git clone \
        --depth 1 \
        --branch missing-include \
        --recurse-submodules \
        https://github.com/aws/aws-sdk-cpp.git

RUN cd aws-sdk-cpp && \
        mkdir build && \
        cd build && \
        cmake -G Ninja -DBUILD_ONLY="core" .. && \
        cmake --build .

Check all that applies:

• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

Check which platforms you have built SDK on to verify the correctness of this PR.

• Linux
• Windows
• Android
• MacOS
• IOS
• Other Platforms

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