Unit test or try building on earliest supported platform versions in CI
Description
I had the podspec validation fail due to
warning: 'scheduledTimerWithTimeInterval:repeats:block:' is only available on iOS 10.0 or newer warning: 'scheduledTimerWithTimeInterval:repeats:block:' is only available on macOS 10.12 or newer
but this error didn't happen anywhere else. It would be nice to have minimum API checks for all the platforms. Usually this happens in Xcode, I'm not sure why this wasn't caught.
Relatedly, I noticed that the github action image providing Xcode 10 is deprecated and will no longer be supported as of 1 Dec 2022 (source). We should either figure out a way to continue testing on that platform, or consider bumping up our minimum supported platform versions to things we can actually test.