Bump dart-lang/setup-dart from 1.5.0 to 1.6.2 #1320

Job	Run time
mono_repo self validate	13s
format_analyze; linux; Dart dev; PKG: benchmarks; `dart format --output=none --set-exit-if-change...	24s
format_analyze; linux; Dart dev; PKG: api_benchmark; `dart format --output=none --set-exit-if-cha...	26s
format_analyze; linux; Dart 2.19.0; PKG: protobuf; `dart analyze lib`, `dart analyze test`	25s
format_analyze; linux; Dart dev; PKG: protobuf; `dart format --output=none --set-exit-if-changed ...	18s
format_analyze; linux; Dart dev; PKG: protoc_plugin; `dart format --output=none --set-exit-if-cha...	31s
run_tests; linux; Dart 2.19.0; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `dart test`	47s
run_tests; linux; Dart 2.19.0; PKG: protobuf; `dart test`	27s
run_tests; linux; Dart dev; PKG: protobuf; `dart test`	30s
run_tests; linux; Dart dev; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `dart test`	37s
run_tests; osx; Dart 2.19.0; PKG: protobuf; `dart test`	1m 4s
run_tests; osx; Dart dev; PKG: protobuf; `dart test`	53s
run_tests; windows; Dart 2.19.0; PKG: protobuf; `dart test`	54s
run_tests; windows; Dart dev; PKG: protobuf; `dart test`	41s
run_legacy_tests; linux; Dart 2.19.0; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `d...	36s
	8m 46s

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