fix: post excerptare generated using only published content that is in use

[guqing]

What type of PR is this?

/kind improvement /area core /milestone 2.0

What this PR does / why we need it:

文章自动摘要只从正在使用的已发布版本的内容中取得

Which issue(s) this PR fixes:

Fixes #2452

Special notes for your reviewer:

/cc @halo-dev/sig-halo

Does this PR introduce a user-facing change?

None

[f2c-ci-robot[bot]]

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