Alpine container error /bin/sh upload.sh not found even after installing bash

I am facing an error when attempting to run a bash script inside an alpine container :

/bin/sh: upload.sh: not found

This is happening despite that I have already installed bash as in the Dockerfile below :

# bash on alpine

FROM quay.io/bashell/alpine:latest
WORKDIR /tmp

# make sure the package repository is up to date
RUN apk update \
 && apk upgrade \
 && apk add bash \
 && rm -rf /var/cache/*/* \
 && echo "" > /root/.ash_history

# change default shell from ash to bash
RUN sed -i -e "s/bin\/ash/bin\/bash/" /etc/passwd

ENV LC_ALL=en_US.UTF-8

# copy in upload.sh
COPY upload.sh .
RUN chmod +x upload.sh
RUN apk update && apk add curl git
RUN curl -LO https://storage.googleapis.com/kubernetes-release/release/v1.15.1/bin/linux/amd64/kubectl
RUN chmod u+x kubectl && mv kubectl /bin/kubectl

The script upload.sh :

#!/bin/bash
touch myfile.txt
FILE=$(pwd)
echo "File is available at $FILE/myfile.txt

"

Output of ls -la :

 /tmp # ls -la
total 16
drwxrwxrwt    1 root     root          4096 Sep 19 14:40 .
drwxr-xr-x    1 root     root          4096 Sep 20 10:14 ..
-rwxr-xr-x    1 root     root            88 Sep 19 14:33 upload.sh

What I have tried :

1. Run and exec into the container

   /tmp # which bash /bin/bash

2. Checked the formatting for upload.sh

Line endings is correct - LF

Encoding is correct - UTF-8

3. Tried using /bin/sh in the script (without and with bash installed) - still getting the same error

4. Tried using /bin/ash in the script (without and with bash installed) - still getting the same error

UPDATE:

I have found that when I exec into the container and run the script as :

sh upload

it executes successfully.

The actual use-case is to run the Docker container (and hence the script) in a K8S environment with the following deployment configuration (Is this correct?) :

apiVersion: v1
kind: Pod
metadata:
  name: alpine
  namespace: labs
spec:
  serviceAccountName: alpine
  containers:
  - image: myuser/alpine-kubectl
    volumeMounts:
            - name: datadir
              mountPath: /tmp
    command:
      - sh
      - "-c"
      - "./upload.sh && sleep 100000000"
    imagePullPolicy: IfNotPresent
    name: alpine
    
  restartPolicy: Always
  volumes:
        - name: datadir
          persistentVolumeClaim:
            claimName: alpine

Is this correct or I should handle the issue at the time I build the Dockerfile?