test: Allow multiple issuer items of the same kind #2527

Job	Run time
Check MSRV	1m 30s
Validate external types appearing in public API	1m 9s
build-windows	2m 8s
Documentation (nightly)	1m 46s
Build rustls-cert-gen as a standalone package	31s
Documentation (stable)	1m 53s
Clippy	13m 30s
Measure coverage	34s
Format (unstable)	14s
Check semver compatibility	1m 7s
build (ubuntu-latest, stable 7 months ago)	12m 56s
build (ubuntu-latest, beta)	12m 22s
build (ubuntu-latest, nightly)	12m 32s
build (ubuntu-latest, stable)	12m 55s
build (macOS-latest, stable)	51s
	1h 15m 58s

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