Fix flaky global ErrorHandler delegation test

[MrAlias]

Remove multi-goroutine approach and just test what needs to be tested. Meaning this:

--- FAIL: TestHandlerTestSuite (0.05s)
    --- FAIL: TestHandlerTestSuite/TestNoDropsOnDelegate (0.01s)
        handler_test.go:121: 
            	Error Trace:	handler_test.go:121
            	Error:      	Received unexpected error:
            	            	no errors sent in 10ms
            	Test:       	TestHandlerTestSuite/TestNoDropsOnDelegate
            	Messages:   	starting error stream
FAIL
coverage: 1.5% of statements in ./...
FAIL	go.opentelemetry.io/otel/api/global	0.172s

should be fixed and not cause false positives.

Resolves #907

[codecov]

Codecov Report

Merging #1829 (e71537f) into main (e43d9c0) will increase coverage by 0.0%.
The diff coverage is n/a.

@@          Coverage Diff          @@
##            main   #1829   +/-   ##
=====================================
  Coverage   78.3%   78.4%           
=====================================
  Files        135     135           
  Lines       7246    7246           
=====================================
+ Hits        5680    5682    +2     
+ Misses      1318    1317    -1     
+ Partials     248     247    -1     

Impacted Files	Coverage Δ
exporters/trace/jaeger/jaeger.go	88.5% <0.0%> (-1.0%)	⬇️
sdk/trace/batch_span_processor.go	83.9% <0.0%> (+1.5%)	⬆️
exporters/otlp/otlpgrpc/connection.go	92.5% <0.0%> (+1.8%)	⬆️

[Aneurysm9]

Merging this with a single approval and prior to 24h as it is straightforward, confined to tests, and will eliminate a pain in our neck for other PRs in flight.