Rust

Restrict the dependency on `indexmap` to v2 only #146

Job	Run time
test (ubuntu-latest, stable, 2.0.0)	37s
test (ubuntu-latest, stable, latest)	42s
test (ubuntu-latest, 1.64.0, 2.0.0)	54s
test (ubuntu-latest, 1.64.0, latest)	44s
test (windows-latest, stable, 2.0.0)	40s
test (windows-latest, stable, latest)	41s
test (windows-latest, 1.64.0, 2.0.0)	40s
test (windows-latest, 1.64.0, latest)	40s
test (macos-latest, stable, 2.0.0)	28s
test (macos-latest, stable, latest)	42s
test (macos-latest, 1.64.0, 2.0.0)	51s
test (macos-latest, 1.64.0, latest)	42s
	8m 21s

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