Fix preview mode handling in cache interceptor

[conico974]

Fix cache interceptor returning cached response when using previiew mode.

Thanks @horai93 for the issue and the fix there.
Fix #919

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	26.58%	2596 / 9764
🔵	Statements	26.58%	2596 / 9764
🔵	Functions	54.26%	140 / 258
🔵	Branches	73.13%	618 / 845

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
packages/open-next/src/core/routing/cacheInterceptor.ts	88.88%	60.71%	100%	88.88%	44, 55-61, 75-76, 120, 174-175, 196-198, 203-204, 215-217, 227-228, 280-281

Generated in workflow #1370 for commit b18b99b by the Vitest Coverage Report Action

[pkg-pr-new]

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commit: b18b99b