fix(services/dropbox): fix dropbox ci #618

Job	Run time
check_clippy	3m 13s
check_docs	2m 48s
build_default_features (ubuntu-latest)	41s
check_msrv	30s
build_default_features (macos-latest)	50s
build_all_features	4m 36s
build_default_features (windows-latest)	1m 53s
build_all_platforms (ubuntu-latest)	2m 17s
build_under_wasm	50s
build_all_platforms (macos-latest)	7m 26s
build_all_platforms (windows-latest)	5m 26s
unit	6m 11s
	36m 41s

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