Make EvalModeConvertible reflexive #1246

Job	Run time
build (ubuntu-latest, nix, false, false, 8107, nix-8107)	12m 10s
build (ubuntu-latest, stack, --stack-yaml stack-lts-18.28-lowerbound.yaml, false, false, 8107, st...	12m 22s
build (ubuntu-latest, nix, false, false, 902, nix-902)	12m 1s
build (ubuntu-latest, nix, false, false, 928, nix-928)	12m 34s
build (ubuntu-latest, nix, false, false, 948, nix-948)	10m 14s
build (ubuntu-latest, nix, false, false, 966, nix-966)	9m 41s
build (ubuntu-latest, nix, false, false, 984, nix-984)	9m 38s
build (ubuntu-latest, nix, true, false, 9101, nix-9101)	10m 2s
build (ubuntu-latest, cabal, false, false, 9121, cabal-9121)	9m 47s
build (macOS-latest, nix, true, false, 9101, nix-9101)	12m 30s
	1h 50m 59s

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