add pnpm to Snapcraft (go-gitea#35778) (go-gitea#35779)

Backport go-gitea#35778 by techknowlogick

Co-authored-by: techknowlogick <techknowlogick@gitea.com>

Author: GiteaBot

snap/snapcraft.yaml

@@ -68,6 +68,7 @@ parts:
     override-build: |
       set -x
       sed -i 's/os.Getuid()/1/g' modules/setting/setting.go
+      npm install -g pnpm
       TAGS="bindata sqlite sqlite_unlock_notify pam cert" make build
       install -D gitea "${SNAPCRAFT_PART_INSTALL}/gitea"
       cp -r options "${SNAPCRAFT_PART_INSTALL}/"