[BACKPORT 1.16] ci: fix failsafe sim

[MaEtUgR]

Solved Problem

When checking 1.16 backport prs (https://github.com/PX4/PX4-Autopilot/pulls?q=is%3Apr+is%3Aopen+1.16) I found that ci is failing because #25739

Solution

Backport it 1:1. It's very low risk, doesn't impact the PX4 build at all but will make ci pass on any prs to 1.16 based branches.

Changelog Entry

ci: Pin emscripten to a version that doesn't warn -> error without C++ 17

Test coverage

It works as expected on main and also on another internal branch where I had this problem and ci should then also pass on this pr.

[MaEtUgR]

Why don't I get a CI build for like e.g. is failing in #25736 ?

[mrpollo]

Because the CI action will only run under the following conditions

on:
  push:
    branches:
    - 'main'
    paths-ignore:
      - 'docs/**'
      - '.github/**'
  pull_request:
    branches:
      - '**'
    paths-ignore:
      - 'docs/**'
      - '.github/**'

[dagar]

Why don't I get a CI build for like e.g. is failing in #25736 ?

The github action configuration.

PX4-Autopilot/.github/workflows/failsafe_sim.yml

Lines 5 to 6 in f32c302

	branches:
	- 'main'

Annoyingly this produces slightly different results for people that push to the main repo then open a pull request vs someone that opens a pull request from a fork.