Update nextjs.yml

add detect package manger for pnpm

Author: yashdev9274

.github/workflows/nextjs.yml

@@ -44,6 +44,11 @@ jobs:
             echo "command=ci" >> $GITHUB_OUTPUT
             echo "runner=npx --no-install" >> $GITHUB_OUTPUT
             exit 0
+          elif [ -f "${{ github.workspace }}/pnpm-lock.yaml" ]; then
+            echo "manager=pnpm" >> $GITHUB_OUTPUT
+            echo "command=install --frozen-lockfile" >> $GITHUB_OUTPUT
+            echo "runner=pnpm" >> $GITHUB_OUTPUT
+            exit 0
           else
             echo "Unable to determine package manager"
             exit 1