fix(deps): update dependency gaxios to v6 - autoclosed

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
gaxios	^5.0.0 -> ^6.0.0

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Release Notes

googleapis/gaxios (gaxios)

### [`v6.0.0`](https://togithub.com/googleapis/gaxios/blob/HEAD/CHANGELOG.md#600-2023-07-12) [Compare Source](https://togithub.com/googleapis/gaxios/compare/v5.1.3...v6.0.0) ##### ⚠ BREAKING CHANGES - add status as a number to GaxiosError, change code to error code as a string ([#​552](https://togithub.com/googleapis/gaxios/issues/552)) - migrate to Node 14 ([#​548](https://togithub.com/googleapis/gaxios/issues/548)) - examine response content-type if no contentType is set ([#​535](https://togithub.com/googleapis/gaxios/issues/535)) ##### Bug Fixes - Add status as a number to GaxiosError, change code to error code as a string ([#​552](https://togithub.com/googleapis/gaxios/issues/552)) ([88ba2e9](https://togithub.com/googleapis/gaxios/commit/88ba2e99e32b66d84725c9ea9ad95152bd1dc653)) - Examine response content-type if no contentType is set ([#​535](https://togithub.com/googleapis/gaxios/issues/535)) ([cd8ca7b](https://togithub.com/googleapis/gaxios/commit/cd8ca7b209f0ba932082a80ace8fec608a71facf)) ##### Miscellaneous Chores - Migrate to Node 14 ([#​548](https://togithub.com/googleapis/gaxios/issues/548)) ([b9b26eb](https://togithub.com/googleapis/gaxios/commit/b9b26eb2c4af35633efd91770aa24c4b5d9019b4))

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