Explicit test requirements of figure_mixed_content

[dginev]

Fixes #2427

This may be a change in the packaging of texlive, I am unsure. I would have assumed our texlive 2021 CI would also fail due to the various .sty dependencies not being present, but it succeeds?

To reproduce the reported error on Ubuntu (with texlive 2023), it takes:

$ sudo apt remove texlive-science

With this PR the test is gracefully skipped:

$ make test TEST_FILES=t/80_complex.t 
PERL_DL_NONLAZY=1 "/usr/bin/perl" "-MExtUtils::Command::MM" "-MTest::Harness" "-e" "undef *Test::Harness::Switches; test_harness(0, 'blib/lib', 'blib/arch')" t/80_complex.t
t/80_complex.t .. 5/15 # Skip: Missing requirement algorithm.sty for t/complex/figure_mixed_content
t/80_complex.t .. 11/15 # Skip: Missing requirement siunitx.sty for t/complex/si
t/80_complex.t .. ok     
All tests successful.

[dginev]

To be precise, the failure condition was triggered on a system where graphicx.sty was available, but algorithm.sty wasn't. Which I assume was due to it moving between texlive packages, but that's speculation.

[brucemiller]

Yeah, explicit requirements seem better than texlive versions (which don't seem very precise).