Quote mirror script path expansions in mirror docs

[Copilot]

Description

This updates the two shell script examples in docs/release-team/mirror-scripts.md to address the review-thread feedback about incomplete quoting. The snippets now consistently quote path and rsync arguments so the documented examples align with the stated shell-safety expectations.

• Archive mirror example

  • Quote BASEDIR in the directory existence check and mkdir -p
  • Quote both RSYNCSOURCE and BASEDIR in the two rsync invocations
  • Quote the full trace-file redirect target

• Release mirror example

  • Apply the same quoting fixes to the directory check, mkdir -p, rsync, and trace-file redirect

• Example

  if [ ! -d "${BASEDIR}" ]; then
    mkdir -p "${BASEDIR}" || fatal "Creation of ${BASEDIR} failed."
  fi
  
  rsync ... "${RSYNCSOURCE}" "${BASEDIR}" || fatal "Failed to rsync from ${RSYNCSOURCE}."
  
  date -u > "${BASEDIR}/.trace/$(hostname -f)"
  

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Related issue

Addressed via the linked PR review thread.

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Checklist

• I have read and followed the Ubuntu Project contributing guide
• My pull request is linked to an existing issue (if applicable)
• I have tested my changes, and they work as expected

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Additional notes (optional)

This change is intentionally limited to the two reviewed documentation snippets and does not modify unrelated content on the page.

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