chore(triagebot): A-json-output for machine_message.rs (#16133)

### What does this PR try to resolve?

`src/cargo/util/machine_message.rs` defines shapes of JSON messages
output, so should be labeled as `A-json-output`. `A-console-output` is
more around styling and the underlying machinery.

Author: epage

triagebot.toml

@@ -105,7 +105,6 @@ trigger_files = ["src/cargo/util/context/mod.rs"]
 [autolabel."A-console-output"]
 trigger_files = [
   "src/cargo/core/shell.rs",
-  "src/cargo/util/machine_message.rs",
   "src/cargo/util/progress.rs",
 ]
 
@@ -171,6 +170,9 @@ trigger_files = [
 [autolabel."A-interacts-with-crates.io"]
 trigger_files = ["crates/crates-io/", "src/cargo/ops/registry/"]
 
+[autolabel."A-json-output"]
+trigger_files = ["src/cargo/util/machine_message.rs"]
+
 [autolabel."A-layout"]
 trigger_files = [
   "src/cargo/core/compiler/build_runner/compilation_files.rs",