fixes for Julia 1.11

[palday]

• ignore versioned manifest
• use public API for accessing the contents of an IOBuffer Skip needing that IOBuffer entirely
• update tests to use static values instead of depending on MersenneTwister, which can (and does) change outputs between Julia versions
• avoid an issue with read(io, typemax(Int)) when reading from a Process on 1.11 (this caused the FLAC tests to fail). (xref readbytes!(::Process, ::Vector{UInt8}, ::Int) does not read bytes on 1.11 JuliaLang/julia#56078)

[omus]

• update tests to use static values instead of depending on MersenneTwister, which can (and does) change outputs between Julia versions

Any reason you decided not to use StableRNGs.jl?

[palday]

• update tests to use static values instead of depending on MersenneTwister, which can (and does) change outputs between Julia versions

Any reason you decided not to use StableRNGs.jl?

Because it was a single short example and it was easier to just use the values that MersenneTwister formerly produced rather than update the test results. This also made it so that the reference values didn't change, which makes it easier to check that I didn't break something else with the changes here.