Update curl/libcurl in DAST validation runner to 8.4.0

Problem

curl will be releasing high severity patch on October 11, 2023 06:00 UTC

• Curl announcement about the issue https://github.com/curl/curl/discussions/12026
• Related to slack thread https://gitlab.slack.com/archives/C8S0HHM44/p1696841338761719
• Related issue: https://gitlab.com/gitlab-com/gl-security/security-department-meta/-/issues/1693

Curl is used by the DAST runner validation to verify that a customer has ownership of the target application prior to running an on-demand scan.

Proposal / Implementation plan

• Upgrade DAST validation runnner curl
• Upgrade DAST validation runner base image version to a more recent version of Alpine
• Release DAST validation runner