docker-publish failed: python3: command not found

When publishing the image in a docker registry, a "skopeo" image is used and calling merge_json function in "gitlab-ci-docker.yml " leading to :

Gitlab job log

$ ( # collapsed multi-line command
$ # BEGSCRIPT # collapsed multi-line command
[INFO] Custom CA certificates imported in /etc/ssl/certs/ca-certificates.crt
/scripts-516489-270967115/step_script: line 534: python3: command not found

The code of the function is

function merge_json() {
    python3 -c "import json,sys
  def merge(a,b):
    for key in b:
      if key in a and isinstance(a[key],dict) and isinstance(b[key],dict): a[key]=merge(a[key],b[key])
      else: a[key]=b[key]
    return a
  def mergef(*files):
    res={}
    for f in files:
      with open(f,'r') as rd: res=merge(res,json.load(rd))
    return res
  print(json.dumps(mergef(*sys.argv[1:])))" "$@"
  }

A python code checker is reporting:

Traceback (most recent call last): ^^^^^^^^^^^ ^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Error on line 2: python3 -c "import json,sys ^ SyntaxError: unterminated string literal (detected at line 2)

Could it be a simply a problem with bad indentation or line continuation interpretation?

For better lisibility, of the function, can we try something like:

python3 -c "
import json, sys

def merge(a, b):
    for key in b:
        if key in a and isinstance(a[key], dict) and isinstance(b[key], dict):
            a[key] = merge(a[key], b[key])
        else:
            a[key] = b[key]
    return a

def mergef(*files):
    res = {}
    for f in files:
        with open(f, 'r') as rd:
            res = merge(res, json.load(rd))
    return res

print(json.dumps(mergef(*sys.argv[1:])))
" "$@"