/bin/sh: eval: line 97: ./mybinary not found

I’m attempting to run a binary artifact in a job that was produced in an earlier job. Here’s the job execution log:

Running with gitlab-runner 11.11.2 (ac2a293c)
  on docker-auto-scale 0277ea0f
Using Docker executor with image alpine ...
Pulling docker image alpine ...
Using docker image sha256:055936d3920576da37aa9bc460d70c5f212028bda1c08c0879aedf03d7a66ea1 for alpine ...
Running on runner-0277ea0f-project-10880841-concurrent-0 via runner-0277ea0f-srm-1560230988-68c05137...
Initialized empty Git repository in /builds/group/repo/.git/
Fetching changes...
Created fresh repository.
From https://gitlab.com/group/repo
 * [new branch]      master     -> origin/master
Checking out b8d63ff7 as master...
Skipping Git submodules setup
Downloading artifacts for compile-linux (228759107)...
Downloading artifacts from coordinator... ok        id=228759107 responseStatus=200 OK token=64hfxDrL
$ mkdir -p $GOPATH/src/$(dirname $REPO_NAME)
'/src/gitlab.com/group/repp' -> '/builds/group/repo'
$ apk add ca-certificates
fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/community/x86_64/APKINDEX.tar.gz
(1/1) Installing ca-certificates (20190108-r0)
Executing busybox-1.29.3-r10.trigger
Executing ca-certificates-20190108-r0.trigger
OK: 6 MiB in 15 packages
$ ls -la ./mybinary
-rwxr-xr-x    1 root     root      12659960 Jun 11 05:30 ./mybinary
$ ./mybinary -app=${APP_ID} -secret=${SECRET} -output=output.ext
/bin/sh: eval: line 97: ./mybinary: not found
ERROR: Job failed: exit code 127

Here’s the .gitlab-ci.yml file:

image: golang:latest

    REPO_NAME: gitlab.com/group/repo

    - mkdir -p $GOPATH/src/$(dirname $REPO_NAME)
    - ln -svf $CI_PROJECT_DIR $GOPATH/src/$REPO_NAME
    - cd $GOPATH/src/$REPO_NAME

    - build
    - run

    stage: build
      - go build -o mybinary
        - mybinary

    stage: run
    image: alpine
      - apk add ca-certificates
      - ls -la ./mybinary
      - ./mybinary -app=${APP_ID} -secret=${SECRET} -output=output.ext

I’m totally stumped as to why it can’t find mybinary, since in the command right before it I used the ls command to print out information about it (and it is executable). Any ideas what’s wrong with my setup?

I got unblocked by using the debian image instead of alpine, but I’d still like to know why it didn’t work with alpine. =/