Refactor tmpl and blob_excerpt (#32967)

1. do not use `{{/* */}}` to remove spaces, use `{{- -}}`
2. fix "blob_excerpt" endpoint, remove the legacy fragile code: have
tested commit diff and wiki diff

templates/repo/release/label.tmpl

@@ -1,5 +1,4 @@
-{{/*
-Template Attributes:
+{{/* Template Attributes:
 * Release: the release
 * IsLatest: boolean indicating whether this is the latest release, optional
 */}}