tests: cover media nosniff header

changelog/fragments/pr-30356.md

@@ -0,0 +1 @@
+- Security/Media route: add `X-Content-Type-Options: nosniff` header regression assertions for successful and not-found media responses (#30356) (thanks @13otKmdr)

src/media/server.test.ts

@@ -61,6 +61,7 @@ describe("media server", () => {
     const file = await writeMediaFile("file1", "hello");
     const res = await fetch(mediaUrl("file1"));
     expect(res.status).toBe(200);
+    expect(res.headers.get("x-content-type-options")).toBe("nosniff");
     expect(await res.text()).toBe("hello");
     await waitForFileRemoval(file);
   });
@@ -113,6 +114,7 @@ describe("media server", () => {
   it("returns not found for missing media IDs", async () => {
     const res = await fetch(mediaUrl("missing-file"));
     expect(res.status).toBe(404);
+    expect(res.headers.get("x-content-type-options")).toBe("nosniff");
     expect(await res.text()).toBe("not found");
   });