Custom Gradle (Alpine) image with curl installed

BitBucket pipeline:
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image: gradle:jdk8-alpine

pipelines:
  custom: # Pipelines that can only be triggered manually
    Build & deploy:
      - step:
          script:
          - cat /etc/passwd
          - id
          - addgroup gradle root
          - apk update && apk add --no-cache --virtual .fetch-deps curl python-dev && apk del .fetch-deps && python --version
          - curl -O https://bootstrap.pypa.io/get-pip.py
          ...
          ...
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Output:
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+ cat /etc/passwd
root:x:0:0:root:/root:/bin/ash
bin:x:1:1:bin:/bin:/sbin/nologin
...
...
nobody:x:65534:65534:nobody:/:/sbin/nologin
gradle:x:1000:1000:Linux User,,,:/home/gradle:/bin/ash

+ id
uid=1000(gradle) gid=1000(gradle) groups=1000(gradle)

+ addgroup gradle root
addgroup: permission denied (are you root?)
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