docgen:integrations: don't strip hashes from links

[mrienstra]

What kind of changes does this PR include?

• Changes to the docs site code (specifically to scripts/generate-integration-pages.ts, which is called by pnpm run docgen:integrations)

Description

• I noticed that a link hash was disappearing somewhere between withastro/astro and withastrodocs`:

  - https://docs.astro.build/en/reference/configuration-reference/#markdownextenddefaultplugins
  +                         /en/reference/configuration-reference/

• Tracked down the source of the issue, this PR fixes it (confirmed locally).
• Also made a very minor change to an unrelated regex in the same script, to reduce the chance of it erroneously matching in the future.
• Tempting to figure out how to test this script, but I gather it will be retired sometime in the next few months.

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[delucis]

Nice catch @mrienstra! I hadn’t realised these fragment links were getting stripped out — thanks for fixing.