[typescript] replace headers with same case-insensitive key to match http spec #109

Job	Run time
Build projects (20.x, samples/client/others/typescript-angular/)	56s
Build projects (20.x, samples/client/petstore/typescript-angular-v20-provided-in-root/)	1m 40s
Build projects (20.x, samples/openapi3/client/petstore/typescript/builds/default/)	1m 1s
Build projects (20.x, samples/client/petstore/typescript-angular-v18-provided-in-root/)	1m 45s
Build projects (20.x, samples/client/petstore/typescript-angular-v17-provided-in-root/)	1m 43s
Build projects (20.x, samples/openapi3/client/petstore/typescript/builds/jquery/)	43s
Build projects (20.x, samples/client/petstore/typescript-angular-v16-provided-in-root/)	1m 32s
Build projects (20.x, samples/client/petstore/typescript-angular-v19-provided-in-root/)	2m 2s
Build projects (20.x, samples/openapi3/client/petstore/typescript/builds/browser/)	1m 0s
Build projects (20.x, samples/client/petstore/typescript-fetch/builds/default/)	44s
Build projects (20.x, samples/client/petstore/typescript-axios/builds/with-npm-version/)	47s
Build projects (20.x, samples/client/petstore/typescript-fetch/tests/default/)	1m 9s
Build projects (20.x, samples/client/petstore/typescript-fetch/builds/with-npm-version/)	1m 2s
Build projects (20.x, samples/openapi3/client/petstore/typescript/builds/object_params/)	46s
Build projects (20.x, samples/client/petstore/typescript-rxjs/builds/with-npm-version/)	59s
Build projects (20.x, samples/client/petstore/typescript-fetch/builds/es6-target/)	54s
	18m 43s

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