fix(deps): update module github.com/hashicorp/terraform-plugin-mux to v0.16.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
github.com/hashicorp/terraform-plugin-mux	v0.15.0 -> v0.16.0

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Release Notes

hashicorp/terraform-plugin-mux (github.com/hashicorp/terraform-plugin-mux)

### [`v0.16.0`](https://togithub.com/hashicorp/terraform-plugin-mux/releases/tag/v0.16.0) [Compare Source](https://togithub.com/hashicorp/terraform-plugin-mux/compare/v0.15.0...v0.16.0) NOTES: - all: The `v0.15.0` release updated this Go module to Go 1.21 per the [Go support policy](https://go.dev/doc/devel/release#policy). It is recommended to review the [Go 1.21 release notes](https://go.dev/doc/go1.21) before upgrading. Any consumers building on earlier Go versions may experience errors ([#​227](https://togithub.com/hashicorp/terraform-plugin-mux/issues/227)) ENHANCEMENTS: - tf5to6server: Add deferred action request and response fields to RPC translations ([#​237](https://togithub.com/hashicorp/terraform-plugin-mux/issues/237)) - tf6to5server: Add deferred action request and response fields to RPC translations ([#​237](https://togithub.com/hashicorp/terraform-plugin-mux/issues/237))

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