fix: enforce content type header for API requests #26311

Job	Run time
Build & cache Go code	2m 55s
Build & cache Go code	2m 55s
Build, test & lint UI code	1m 35s
Build, test & lint UI code	1m 35s
Ensure Go modules synchronicity	15s
Ensure Go modules synchronicity	15s
Check changes to generated code	8m 21s
Check changes to generated code	8m 21s
Lint Go code	2m 11s
Lint Go code	2m 11s
Run unit tests with -race for Go packages	7m 53s
Run unit tests with -race for Go packages	7m 53s
Run unit tests for Go packages	11m 39s
Run unit tests for Go packages	3m 58s
Run end-to-end tests (v1.28.2)	30m 9s
Run end-to-end tests (v1.28.2)	45m 24s
Run end-to-end tests (v1.27.6)	30m 7s
Run end-to-end tests (v1.27.6)	45m 36s
Run end-to-end tests (v1.26.9)	30m 7s
Run end-to-end tests (v1.26.9)	45m 28s
Run end-to-end tests (v1.25.14)	30m 9s
Run end-to-end tests (v1.25.14)	44m 19s
Process & analyze test artifacts	0s
Process & analyze test artifacts	32s
	6h 3m 48s

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