Update emoji set to Unicode 15 (#25595)

Update emoji set to Unicode 15 which was added upstream here:
cb5c514d47

<img width="854" alt="Screenshot 2023-06-29 at 11 02 56 AM"
src="https://github.com/go-gitea/gitea/assets/1669571/7bfb663d-0804-4d23-a62d-f585a6783ca6">

---------

Co-authored-by: silverwind <me@silverwind.io>

.github/workflows/files-changed.yml

@@ -39,6 +39,7 @@ jobs:
             backend:
               - "**/*.go"
               - "templates/**/*.tmpl"
+              - "assets/emoji.json"
               - "go.mod"
               - "go.sum"
               - "Makefile"
@@ -46,6 +47,7 @@ jobs:
             frontend:
               - "**/*.js"
               - "web_src/**"
+              - "assets/emoji.json"
               - "package.json"
               - "package-lock.json"
               - "Makefile"