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>

trace/span_test.go

@@ -4,7 +4,6 @@
 package trace
 
 import (
-	"context"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -91,7 +90,7 @@ func TestLinkFromContext(t *testing.T) {
 	k1v1 := attribute.String("key1", "value1")
 	spanCtx := SpanContext{traceID: TraceID([16]byte{1}), remote: true}
 
-	receiverCtx := ContextWithRemoteSpanContext(context.Background(), spanCtx)
+	receiverCtx := ContextWithRemoteSpanContext(t.Context(), spanCtx)
 	link := LinkFromContext(receiverCtx, k1v1)
 
 	if !assertSpanContextEqual(link.SpanContext, spanCtx) {