Add 32-bit Linux CI coverage

[danyalahmed1995]

Adds a 32-bit Ubuntu CI matrix entry using gcc/g++ multilib and -m32 flags.

The sample build is skipped for this cross-compilation entry to avoid requiring 32-bit graphics/system libraries, while header generation and the unit test builds still run across the supported C++ standards.

This covers the Linux 32-bit CI case discussed in #2584 and helps exercise the kind of build configuration involved in #2583.

Tested on my fork:

• CI Build / ubuntu-24.04 x86, Ninja, g++-14 passed
• Full fork PR checks passed

Refs #2584.

[CLAassistant]

All committers have signed the CLA.

[M2-TE]

Good addition, thanks for the contribution!
Just got a few comments regarding the addition of new options in the matrix entry.

[sharadhr]

I would also recommend using Clang with --target=i686-linux-gnu.

[danyalahmed1995]

@sharadhr I went with gcc/g++ plus -m32 because it matched the existing Ubuntu GCC matrix entries closely and kept the first 32-bit Linux job minimal. It also passed in my fork before opening the PR.

But if you want the CI entry to model cross-compilation more explicitly, I can switch it to Clang with --target=i686-linux-gnu.