Reduce workflow timeout from default 360 minutes to 15

[gojimmypi]

Ensures workflow tests abort early when stuck.

On two of my recent pull requests, the workflow got stuck here:

Run sudo apt-get install -y gcc-arm-none-eabi
Reading package lists...
Building dependency tree...
Reading state information...
The following additional packages will be installed:
  binutils-arm-none-eabi libnewlib-arm-none-eabi libnewlib-dev
  libstdc++-arm-none-eabi-dev libstdc++-arm-none-eabi-newlib
Suggested packages:
  libnewlib-doc
The following NEW packages will be installed:
  binutils-arm-none-eabi gcc-arm-none-eabi libnewlib-arm-none-eabi
  libnewlib-dev libstdc++-arm-none-eabi-dev libstdc++-arm-none-eabi-newlib
0 upgraded, 6 newly installed, 0 to remove and 21 not upgraded.
Need to get 574 MB of archives.
After this operation, 3106 MB of additional disk space will be used.
Get:1 file:/etc/apt/apt-mirrors.txt Mirrorlist [144 B]
Get:2 http://azure.archive.ubuntu.com/ubuntu noble/universe amd64 binutils-arm-none-eabi amd64 2.42-1ubuntu1+23 [3137 kB]
Get:3 http://azure.archive.ubuntu.com/ubuntu noble/universe amd64 gcc-arm-none-eabi amd64 15:13.2.rel1-2 [57.5 MB]
Get:4 http://azure.archive.ubuntu.com/ubuntu noble/universe amd64 libstdc++-arm-none-eabi-dev all 15:13.2.rel1-2+26 [1320 kB]
Get:5 http://azure.archive.ubuntu.com/ubuntu noble/universe amd64 libnewlib-dev all 4.4.0.20231231-2 [140 kB]
Get:6 http://azure.archive.ubuntu.com/ubuntu noble/universe amd64 libnewlib-arm-none-eabi all 4.4.0.20231231-2 [49.2 MB]
Get:7 http://azure.archive.ubuntu.com/ubuntu noble/universe amd64 libstdc++-arm-none-eabi-newlib all 15:13.2.rel1-2+26 [463 MB]

See also this example that ran for over 2 hours, similarly stuck, before I canceled it.

During this PR, job was stick again. See this one. Problem only today? Longer timeout?