I2I: Relax CSS Limit from 75000 bytes to 100000 bytes

### Summary

Increase the allowed bytes for a valid AMP document with 25%, from 75000 to 100000.
This request is based on a precedent feature request in 2020 https://github.com/ampproject/amphtml/issues/26466
5 years later since the last limit change, the technology has moved forward in terms of hardware, infrastructure and user demand.

Design document
The change itself is quite straightforward, change max_bytes from 75000 to 100000 [here](https://github.com/ampproject/amphtml/blob/master/validator/validator-main.protoascii).

css_length_spec: {
html_format: AMP
max_bytes: 100000
max_bytes_per_inline_style: 1000
}

### Design Document

Same as https://github.com/ampproject/amphtml/issues/26466

### Motivation

Motivation
5 years later since the last limit change, the technology has moved forward in terms of hardware, infrastructure and user demand.
AMP should give a bit more room for CSS in order to keep up with the needs.

Same motivation as https://github.com/ampproject/amphtml/issues/26466

### Alternative Solutions

N/A

### Launch Tracker

_No response_

### Notifications

/cc @ampproject/wg-approvers

Open validator/validator-main.protoascii and locate the AMP css_length_spec entry. Update its max_bytes value from 75000 to 100000, then verify that AMP CSS validation accepts documents up to the new limit.

Written by the indexing model from the issue text.