fix(test): add a `sleep` to `TestLoadToStream`

[agilgur5]

Motivation

• it very infrequently has a test flake in it
  • have had this in my git stash since at least September, and only hit this a few times in those ~9 months
    • I thought it had been fixed by some other changes (#11753 in particular) for a while, but just experienced it again, so nope

Error log:

--- FAIL: TestLoadToStream (0.01s)
    --- FAIL: TestLoadToStream/Success (0.01s)
        load_to_stream_test.go:99: 
            	Error Trace:	/home/runner/work/argo-workflows/argo-workflows/workflow/artifacts/common/load_to_stream_test.go:99
            	Error:      	Not equal: 
            	            	expected: 25
            	            	actual  : 26
            	Test:       	TestLoadToStream/Success

Modifications

• also fix incorrect comment in when.go -- defaultTimeout defaults to 60s, not 30s

Verification

Test passes more often