test: correct resize response content-type to image/jpeg (#391)

The resize routes in workload_mix_realworld declared
"http-resp-content-type": "image/png", but resize_image.wasm.so emits
JPEG (sod_img_save_as_jpeg), so the label was wrong. Confirmed by the
standalone image_resize test, which uses image/jpeg and whose output
matches expected_result.jpg byte-for-byte. Align all six resize routes
with the actual output.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: bushidocodes

tests/workload_mix_realworld/spec.json

@@ -200,47 +200,47 @@
 				"path": "resize_image.wasm.so",
 				"expected-execution-us": 138903,
 				"relative-deadline-us": 208354,
-				"http-resp-content-type": "image/png",
+				"http-resp-content-type": "image/jpeg",
 				"admissions-percentile": 90
 			},
 			{
 				"route": "/resize_1.6",
 				"path": "resize_image.wasm.so",
 				"expected-execution-us": 138903,
 				"relative-deadline-us": 222245,
-				"http-resp-content-type": "image/png",
+				"http-resp-content-type": "image/jpeg",
 				"admissions-percentile": 90
 			},
 			{
 				"route": "/resize_1.7",
 				"path": "resize_image.wasm.so",
 				"expected-execution-us": 138903,
 				"relative-deadline-us": 236135,
-				"http-resp-content-type": "image/png",
+				"http-resp-content-type": "image/jpeg",
 				"admissions-percentile": 90
 			},
 			{
 				"route": "/resize_1.8",
 				"path": "resize_image.wasm.so",
 				"expected-execution-us": 138903,
 				"relative-deadline-us": 250025,
-				"http-resp-content-type": "image/png",
+				"http-resp-content-type": "image/jpeg",
 				"admissions-percentile": 90
 			},
 			{
 				"route": "/resize_1.9",
 				"path": "resize_image.wasm.so",
 				"expected-execution-us": 138903,
 				"relative-deadline-us": 263916,
-				"http-resp-content-type": "image/png",
+				"http-resp-content-type": "image/jpeg",
 				"admissions-percentile": 90
 			},
 			{
 				"route": "/resize_2.0",
 				"path": "resize_image.wasm.so",
 				"expected-execution-us": 138903,
 				"relative-deadline-us": 277806,
-				"http-resp-content-type": "image/png",
+				"http-resp-content-type": "image/jpeg",
 				"admissions-percentile": 90
 			}
 		]