Try to:
<img src="{{ page.url }}/{{ (team.url|first).name }}" class="img-fluid">
Handling images via the file field is more complex than using filepicker or even pagemediaselect.
In my opinion, I would not use the word 'url' for the image, since it is used to call the path of the images. I propose the following.
First in your blueprint the following (change 'url' to 'image'):
.image:
type: filepicker
folder: 'self@'
label: Select a file
preview_images: true
accept:
- .png
- .jpg
Now your .md file would look like this:
title: Teams
body_classes: modular
description: 'Description'
images:
-
person_name: Pedro
role: Developer
person_description: 'Entusiasta de Grav'
image: image.png
alt: Alt description
Second, in your twig template the following:
{% for people in page.header.images %}
{% set image = page.media[people.image] %}
<div class="col-sm-6 col-lg-3 text-center mt-2">
<img src="{{ image.url|e }}" class="img-fluid">
<h3>{{ people.person_name }}</h3>
<p>{{ people.role }}</p>
<p>{{ people.person_description }}</p>
</div>
{% endfor %}