fix(deps): update module github.com/ibm/go-sdk-core/v5 to v5.18.1

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
github.com/IBM/go-sdk-core/v5	v5.17.5 -> v5.18.1

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Release Notes

IBM/go-sdk-core (github.com/IBM/go-sdk-core/v5)

### [`v5.18.1`](https://redirect.github.com/IBM/go-sdk-core/releases/tag/v5.18.1) [Compare Source](https://redirect.github.com/IBM/go-sdk-core/compare/v5.18.0...v5.18.1) ##### Bug Fixes - fix minor problem with debug message ([#​231](https://redirect.github.com/IBM/go-sdk-core/issues/231)) ([cf84c9d](https://redirect.github.com/IBM/go-sdk-core/commit/cf84c9d32b34d0d1132ab4deb27b998d182e2c58)) ### [`v5.18.0`](https://redirect.github.com/IBM/go-sdk-core/releases/tag/v5.18.0) [Compare Source](https://redirect.github.com/IBM/go-sdk-core/compare/v5.17.5...v5.18.0) ##### Features - **IamAssumeAuthenticator:** introduce new authenticator type ([#​229](https://redirect.github.com/IBM/go-sdk-core/issues/229)) ([df85f15](https://redirect.github.com/IBM/go-sdk-core/commit/df85f1516a6c1d5c7884f2614dc70404709c4423))

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