fix: strip trailing slash from issuer URL in OAuth metadata serialization #883

Job	Run time
checks / pre-commit	37s
checks / readme-snippets	10s
checks / test (3.10, lowest-direct, ubuntu-latest)	58s
checks / test (3.11, locked, ubuntu-latest)	54s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 6s
checks / test (3.10, locked, windows-latest)	2m 17s
checks / test (3.10, locked, ubuntu-latest)	53s
checks / test (3.11, lowest-direct, windows-latest)	2m 42s
checks / test (3.10, lowest-direct, windows-latest)	3m 5s
checks / test (3.12, locked, ubuntu-latest)	58s
checks / test (3.12, lowest-direct, windows-latest)	3m 23s
checks / test (3.13, lowest-direct, ubuntu-latest)	56s
checks / test (3.11, lowest-direct, ubuntu-latest)	54s
checks / test (3.13, locked, ubuntu-latest)	41s
checks / test (3.13, locked, windows-latest)	2m 28s
checks / test (3.14, locked, windows-latest)	3m 15s
checks / test (3.14, lowest-direct, windows-latest)	2m 32s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 14s
checks / test (3.14, locked, ubuntu-latest)	2m 22s
checks / test (3.11, locked, windows-latest)	2m 30s
checks / test (3.12, locked, windows-latest)	3m 12s
checks / test (3.13, lowest-direct, windows-latest)	2m 39s
all-green	6s
	39m 52s

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