Add unitary version

Author: oxinabox

src/ChainRulesTestUtils.jl

@@ -23,6 +23,8 @@ function __init__()
     # Try to disable backtrace scrubbing so that full failures are shown
     try
         isdefined(Test, :scrub_backtrace) || error("Test.scrub_backtrace not defined")
+        # depending on julia version or one or the other of these will be hit
+        @eval Test scrub_backtrace(bt,) = bt  # make it do nothing
         @eval Test scrub_backtrace(bt, file_ts, file_t) = bt  # make it do nothing
     catch err
         @warn "Failed to monkey=patch scrub_backtrace. Code is functional but stacktraces may be less useful" exception=(err, catch_backtrace())