fix(compiler-sfc): fix template expression assignment codegen for script setup let refs (#3626)

fix #3625

packages/compiler-core/src/transforms/transformExpression.ts

@@ -143,14 +143,14 @@ export function processExpression(
           // let is a local non-ref value, and we need to replicate the
           // right hand side value.
           // x = y --> isRef(x) ? x.value = y : x = y
-          const rVal = (parent as AssignmentExpression).right
+          const { right: rVal, operator } = parent as AssignmentExpression
           const rExp = rawExp.slice(rVal.start! - 1, rVal.end! - 1)
           const rExpString = stringifyExpression(
             processExpression(createSimpleExpression(rExp, false), context)
           )
           return `${context.helperString(IS_REF)}(${raw})${
             context.isTS ? ` //@ts-ignore\n` : ``
-          } ? ${raw}.value = ${rExpString} : ${raw}`
+          } ? ${raw}.value ${operator} ${rExpString} : ${raw}`
         } else if (isUpdateArg) {
           // make id replace parent in the code range so the raw update operator
           // is removed