MySQL not found in Docker container

I am currently working adding Docker support to one of my apps. I feel like I am really close. The Docker container builds fine with no errors but when I try to run the database migrations within the container, I get this error:

Error Output:
================
sh: 1: mysql: not found

Any help would be appreciated.

docker-compose.yml

version: '3'
services:

  #PHP Service
  app:
    build:
      context: .
      dockerfile: Dockerfile
    image: schierproducts/grease-monkey
    container_name: app
    restart: unless-stopped
    tty: true
    environment:
      APP_ENV: local
      APP_DEBUG: 1
      DB_DATABASE: greasemonkey
      SERVICE_NAME: app
      SERVICE_TAGS: dev
    working_dir: /var/www
    volumes:
      - ./:/var/www
      - ./docker/php/local.ini:/usr/local/etc/php/conf.d/local.ini
    networks:
      - app-network
    depends_on:
      - db

  #Nginx Service
  webserver:
    image: nginx:alpine
    container_name: webserver
    restart: unless-stopped
    tty: true
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - ./:/var/www
      - ./docker/nginx/conf.d/:/etc/nginx/conf.d/
    networks:
      - app-network

  #MySQL Service
  db:
    image: mysql:8.0.23
    container_name: db
    restart: unless-stopped
    tty: true
    ports:
      - "3306:3306"
    environment:
      MYSQL_DATABASE: greasemonkey
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_USER: homestead
      MYSQL_PASSWORD: secret
      SERVICE_TAGS: dev
      SERVICE_NAME: mysql
    networks:
      - app-network
    volumes:
      - dbdata:/var/lib/mysql-files
      - ./docker/mysql/my.cnf:/etc/mysql/my.cnf
      - ./docker/db/init:/docker-entrypoint-initdb.d/:ro

  #Redis Service
  redis:
    image: redis:alpine
    ports:
      - '6379:6379'
    volumes:
      - redisdata:/data
    networks:
      - app-network
    healthcheck:
      test: [ "CMD", "redis-cli", "ping" ]

#Docker Networks
networks:
  app-network:
    driver: bridge

#Volumes
volumes:
  dbdata:
    driver: local
  redisdata:
    driver: local

Dockerfile

FROM php:7.4.14-fpm

# Copy composer.lock and composer.json
COPY composer.lock composer.json /var/www/

# Set working directory
WORKDIR /var/www

# Install dependencies
RUN apt-get update && apt-get install -y \
    gnupg gosu curl ca-certificates zip unzip git supervisor sqlite3 libcap2-bin python2 yarn libzip-dev \
    libfreetype6-dev \
    libjpeg62-turbo-dev \
    libpng-dev

# Clear cache
RUN apt-get clean && rm -rf /var/lib/apt/lists/*

# Install extensions
RUN docker-php-ext-install mysqli pdo pdo_mysql zip exif pcntl
RUN docker-php-ext-enable pdo_mysql mysqli
RUN docker-php-ext-configure gd --with-freetype --with-jpeg
RUN docker-php-ext-install gd

# Install composer
RUN curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer

# Add user for laravel application
RUN groupadd -g 1000 www
RUN useradd -u 1000 -ms /bin/bash -g www www

# Copy existing application directory contents
COPY . /var/www
COPY docker/start.sh /usr/local/bin/start

# Copy existing application directory permissions
COPY --chown=www:www . /var/www

# Updates permissions and runs start command
USER root
RUN chmod u+x /usr/local/bin/start
CMD [ "/usr/local/bin/start" ]

# Change current user to www
USER www

# Expose port 9000 and start php-fpm server
EXPOSE 9000
CMD ["php-fpm"]

My .env file:

DB_HOST=db
DB_PORT=3306
DB_DATABASE=greasemonkey
DB_USERNAME=homestead
DB_PASSWORD=secret