TST: Set subprocess timeouts consistently on CI - #32198

PR summary

Some places do, and some places don't, increase the timeout when running on CI. Instead of having that accidental inconsistency, increase the timeout for everything in the helper function.

For example, I've just now seen test_dpi_change_triggers_resize fail, and it has a fixed timeout of 60 instead of raising it to 120 like other tests.

AI Disclosure

None

PR quality check

• Use an expressive title, e.g. "Fix title font property precedence"
• New and changed code is tested
• [n/a] Plotting related features are demonstrated in an example
• [n/a] New features and API changes have release notes
• [n/a] Documentation complies with general and docstring guidelines