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ARROW-9823: [CI][C++][MinGW] Enable S3

But arrow-s3fs-test is disabled for now. Because the current
aws-sdk-cpp MSYS2 package provides only static library. We can enable
arrow-s3fs-test once aws-sdk-cpp MSYS2 package provides shared
library. See the comment in ci/scripts/cpp_test.sh for details.

Closes #8021 from kou/ci-cpp-mingw-enable-s3

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>