Add `seen_current` to kv #4396

Job	Run time
check examples (ubuntu-latest / stable)	48s
check docs (ubuntu-latest / stable)	1m 10s
check format (ubuntu-latest / nightly)	12s
check feature flags (ubuntu-latest / stable)	5m 28s
check licenses (ubuntu-latest / stable)	21s
check linter (ubuntu-latest / stable)	1m 19s
check minimal versions of transitive dependencies (ubuntu-latest / stable)	26s
check minimal supported rust version (ubuntu-latest / msrv)	19s
check spelling (ubuntu-latest / nightly)	5m 14s
test (ubuntu-latest / stable)	5m 31s
test (macos-latest / stable)	5m 28s
test (windows-latest / stable)	5m 21s
	31m 37s

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