refactor: replace context.Background() with t.Context()/b.Context() in tests (#7352)

Based on the Go version we currently use, the dependency already
supports 1.24+, which allows using `t.Context()` and `b.Context()` in
unit tests and benchmarks respectively.

- Enable `context-background` and `context-todo` in
[`usetesting`](https://golangci-lint.run/docs/linters/configuration/#usetesting)
- Adjust the code to support linter detection

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Tyler Yahn <codingalias@gmail.com>
Co-authored-by: Damien Mathieu <42@dmathieu.com>

sdk/trace/span_limits_test.go

@@ -139,7 +139,7 @@ func testSpanLimits(t *testing.T, limits SpanLimits) ReadOnlySpan {
 	tp := NewTracerProvider(WithRawSpanLimits(limits), WithSpanProcessor(rec))
 	tracer := tp.Tracer("testSpanLimits")
 
-	ctx := context.Background()
+	ctx := t.Context()
 	a := []attribute.KeyValue{attribute.Bool("one", true), attribute.Bool("two", true)}
 	l := trace.Link{
 		SpanContext: trace.NewSpanContext(trace.SpanContextConfig{