Update CHANGELOG.md for 12.9.0

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Update CHANGELOG.md for 12.9.0
9c450782 · GitLab Release Tools Bot · ae4ef817 · ae4ef817 · ae4ef817 · ae4ef817
Commit 9c450782 authored 4 years ago by GitLab Release Tools Bot
--- a/changelogs/unreleased/validate-subnets-field.yml
+++ b/changelogs/unreleased/validate-subnets-field.yml
--- a/changelogs/unreleased/validate_service_project_id_nil_if_template.yml
+++ b/changelogs/unreleased/validate_service_project_id_nil_if_template.yml
--- a/changelogs/unreleased/vh-snippets-content-types.yml
+++ b/changelogs/unreleased/vh-snippets-content-types.yml
--- a/changelogs/unreleased/vh-snippets-finder-tweak.yml
+++ b/changelogs/unreleased/vh-snippets-finder-tweak.yml