fix: handle missing vary header values (#4031) #15958

Job	Run time
Lint	30s
Test with Node.js 20 compiled --without-intl	45m 19s
Test with Node.js 22 compiled --without-intl	10m 47s
Test with Node.js 23 compiled --without-intl	16m 47s
dependency-review	0s
Fuzzing	3m 23s
Test with SQLite enabled	24s
Test TypeScript types	29s
test (20, macos-latest) / Test with Node.js 20 on macos-latest	3m 44s
test (20, ubuntu-latest) / Test with Node.js 20 on ubuntu-latest	3m 39s
test (20, windows-latest) / Test with Node.js 20 on windows-latest	5m 21s
test (22, macos-latest) / Test with Node.js 22 on macos-latest	3m 3s
test (22, ubuntu-latest) / Test with Node.js 22 on ubuntu-latest	4m 5s
test (22, windows-latest) / Test with Node.js 22 on windows-latest	5m 43s
test (23, macos-latest) / Test with Node.js 23 on macos-latest	3m 12s
test (23, ubuntu-latest) / Test with Node.js 23 on ubuntu-latest	3m 38s
test (23, windows-latest) / Test with Node.js 23 on windows-latest	1m 52s
automerge	0s
	1h 51m 56s

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