fix(compiler-ssr): only inject fallthrough attrs for root transition/keep-alive

packages/compiler-ssr/__tests__/ssrComponent.spec.ts

@@ -290,6 +290,25 @@ describe('ssr: components', () => {
         }"
       `)
 
+      // should inject attrs if root with coomments
+      expect(compile(`<!--root--><transition><div/></transition>`).code)
+        .toMatchInlineSnapshot(`
+        "const { ssrRenderAttrs: _ssrRenderAttrs } = require(\\"vue/server-renderer\\")
+
+        return function ssrRender(_ctx, _push, _parent, _attrs) {
+          _push(\`<!--[--><!--root--><div\${_ssrRenderAttrs(_attrs)}></div><!--]-->\`)
+        }"
+      `)
+
+      // should not inject attrs if not root
+      expect(compile(`<div/><transition><div/></transition>`).code)
+        .toMatchInlineSnapshot(`
+        "
+        return function ssrRender(_ctx, _push, _parent, _attrs) {
+          _push(\`<!--[--><div></div><div></div><!--]-->\`)
+        }"
+      `)
+
       expect(compile(`<keep-alive><foo/></keep-alive>`).code)
         .toMatchInlineSnapshot(`
         "const { resolveComponent: _resolveComponent } = require(\\"vue\\")