Permission denied while executing binaries in tmp folder (Docker)

Hello I am trying to build an image which can compile and run a c++ program securely.

FROM golang:latest as builder

WORKDIR /app
COPY . .

RUN go mod download
RUN env CGO_ENABLED=0 go build -o /worker

FROM alpine:latest
RUN apk update && apk add --no-cache g++ && apk add --no-cache tzdata
ENV TZ=Asia/Kolkata

WORKDIR /

COPY --from=builder worker /bin

ARG USER=default
RUN addgroup -S $USER && adduser -S $USER -G $USER

USER $USER

ENTRYPOINT [ "worker" ]

version: "3.9"
services:
  gpp:
    build: .
    environment:
      - token=test_token
      - code=#include <iostream>rnrnusing namespace std;rnrnint main() {rn   int a = 10;rn   int b = 20;rn   cout << a << " " << b << endl;rn   int temp = a;rn   a = b;rn   b = temp;rn   cout << a << " " << b << endl;rn   return 0;rn}
    network_mode: bridge
    privileged: false
    read_only: true
    tmpfs: /tmp
    security_opt:
      - "no-new-privileges"
    cap_drop:
      - "all"

Here worker is a golang binary which reads code from environment variable and stores it in /tmp folder as main.cpp, and then tries to compile and run it using g++ /tmp/main.cpp && ./tmp/a.out (using golang exec)

I am getting this error scratch_4-gpp-1 | Error : fork/exec /tmp/a.out: permission denied, from which what I can understand / know that executing anything from tmp directory is restricted.

Since, I am using read_only root file system, I can only work on tmp directory, Please guide me how I can achieve above task keeping my container secured.