fix(server): remove platform-dependent MIME type assertion for .log artifacts

Signed-off-by: nakatani-yo <yoshihito.nakatani@craftsman-software.com>

Author: nakatani-yo

server/artifacts/artifact_server_test.go

@@ -492,7 +492,9 @@ func TestArtifactServer_GetArtifactFile(t *testing.T) {
 			path:        "/artifact-files/my-ns/workflows/my-wf/my-node-1/outputs/main-logs",
 			statusCode:  200,
 			isDirectory: false,
-			contentType: "text/plain; charset=utf-8", // .log is not in the MIME db on all platforms → fallback
+			// .log may resolve to "text/x-log" where the system MIME db has it,
+			// or fall back to "text/plain" on minimal images. Either is fine;
+			// the non-empty assertion below covers both cases.
 		},
 	}