Flaky test: `TestBackoffRetryCanceledContext` in `exporters/otlp/otlptrace/otlptracegrpc`

[MrAlias]

--- FAIL: TestBackoffRetryCanceledContext (0.00s)
    retry_test.go:170: 
        	Error Trace:	/Users/runner/work/opentelemetry-go/opentelemetry-go/exporters/otlp/otlptrace/otlptracegrpc/internal/retry/retry_test.go:170
        	Error:      	Not equal: 
        	            	expected: 1
        	            	actual  : 2
        	Test:       	TestBackoffRetryCanceledContext
FAIL
FAIL	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc/internal/retry	0.507s
ok  	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc/internal/x	0.388s
FAIL
make: *** [test/./exporters/otlp/otlptrace/otlptracegrpc] Error 1

[MrAlias]

example failure: https://github.com/open-telemetry/opentelemetry-go/actions/runs/19969686835/job/57270918379?pr=7667

[MrAlias]

Duplicate of #7673. Both test and cause are from generated code that, when addressed, will address both tests.