Fix substring matches in WWW-Authenticate parsing #3331

Job	Run time
checks / readme-snippets	13s
checks / pre-commit	51s
checks / test (3.10, locked, windows-latest)	1m 54s
checks / test (3.13, locked, ubuntu-latest)	1m 7s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 14s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 17s
checks / test (3.13, locked, windows-latest)	1m 46s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 8s
checks / test (3.14, locked, ubuntu-latest)	2m 7s
checks / test (3.12, lowest-direct, windows-latest)	1m 45s
checks / test (3.10, locked, ubuntu-latest)	1m 18s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 1s
checks / test (3.10, lowest-direct, windows-latest)	1m 54s
checks / test (3.12, locked, windows-latest)	1m 52s
checks / test (3.14, lowest-direct, windows-latest)	1m 35s
checks / test (3.13, lowest-direct, windows-latest)	1m 52s
checks / test (3.12, locked, ubuntu-latest)	1m 35s
checks / test (3.11, locked, ubuntu-latest)	1m 13s
checks / test (3.11, locked, windows-latest)	2m 10s
checks / test (3.14, locked, windows-latest)	2m 42s
checks / test (3.11, lowest-direct, windows-latest)	1m 52s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 17s
checks / docs	46s
all-green	5s
	34m 34s

Provide feedback