fix: detect prerelease tags of the checked out commit

The default end tag was determined by listing all tags and filtering out prereleases. As a result the currently built
prerelease tag was never evaluated and the changelog was generated for the previous stable release instead. The end tag
is now the tag of the checked out commit, so the prerelease annotation is set as expected. Prerelease filtering remains
in place for the start tag only. Additionally the changelog is no longer skipped for prereleases, since consumers of the
chart benefit from the changes list before the stable release.

Co-authored-by: Copilot <copilot@github.com>

add-annotations.sh

@@ -23,8 +23,9 @@ if [[ ! -f "${CHART_FILE}" ]]; then
   exit 1
 fi
 
-# Determine old and new tags
-DEFAULT_NEW_TAG="$(git tag --sort=-version:refname | grep --invert-match --perl-regexp "${PRERELEASE_PATTERN}" | head --lines 1)"
+# Determine old and new tags. The new tag is the currently checked out one - including prereleases - so that
+# prereleases are detected. Only the old tag is restricted to stable releases.
+DEFAULT_NEW_TAG="$(git describe --tags --exact-match HEAD 2>/dev/null || git tag --sort=-version:refname | head --lines 1)"
 DEFAULT_OLD_TAG="$(git tag --sort=-version:refname | grep --invert-match --perl-regexp "${PRERELEASE_PATTERN}" | head --lines 2 | tail --lines 1)"
 
 if [[ -n "${INPUT_OLD_TAG:-}" ]]; then
@@ -50,9 +51,7 @@ if [[ -z "$(git tag --list "${NEW_TAG}")" ]]; then
 fi
 
 if [[ "${NEW_TAG}" =~ ${PRERELEASE_PATTERN} ]]; then
-  echo "INFO: Tag '${NEW_TAG}' is a prerelease, setting prerelease annotation and skipping changelog."
   yq --no-colors --inplace ".annotations.\"artifacthub.io/prerelease\" = \"true\" | sort_keys(.)" "${CHART_FILE}"
-  exit 0
 fi
 
 CHANGE_LOG_YAML="$(mktemp)"