Update vitest monorepo to ^2.1.6 (#2828) #9419

Job	Run time
Checks and variables	2m 3s
Unit Tests	47s
NJS Unit Tests	15s
Build Binary	31s
Build Plus images / build	1m 43s
Build OSS images (nginx, linux/arm64, linux/amd64) / build	1m 22s
Build OSS images (ngf, linux/arm64, linux/amd64) / build	1m 21s
Helm Tests	0s
Conformance tests (nginx, v1.25.16, true) / Run Tests	6m 47s
Conformance tests (nginx, v1.25.16, false) / Run Tests	6m 31s
Conformance tests (nginx, v1.31.2, true) / Run Tests	6m 37s
Conformance tests (nginx, v1.31.2, false) / Run Tests	6m 41s
Conformance tests (plus, v1.25.16, false) / Run Tests	6m 16s
Conformance tests (plus, v1.25.16, true) / Run Tests	6m 28s
Conformance tests (plus, v1.31.2, false) / Run Tests	6m 41s
Conformance tests (plus, v1.31.2, true) / Run Tests	6m 18s
Functional tests (nginx, v1.25.16) / Run Tests	14m 23s
Functional tests (nginx, v1.31.2) / Run Tests	13m 35s
Package and Publish Helm Chart	0s
Functional tests (plus, v1.25.16) / Run Tests	13m 15s
Functional tests (plus, v1.31.2) / Run Tests	13m 15s
	1h 54m 49s

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