test: use t.Context() instead of context.Background() (#1306)

The test context is cancelled when the test ends, so anything still holding it stops instead of leaking into the next test. Uses inside `t.Cleanup`, `defer` and `go func` blocks are left alone, as the context is already cancelled there.

Stacked on https://gitea.com/gitea/runner/pulls/1305.

Assisted-by: Codet
Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1306
Reviewed-by: bircni <[email protected]>

internal/app/cmd/exec_test.go

@@ -5,7 +5,6 @@ package cmd
 
 import (
 	"bytes"
-	"context"
 	"io"
 	"os"
 	"path/filepath"
@@ -217,7 +216,7 @@ func TestPrintListReportsDuplicateJobIDs(t *testing.T) {
 }
 
 func TestLoadExecCmdDefinesExpectedFlags(t *testing.T) {
-	cmd := loadExecCmd(context.Background())
+	cmd := loadExecCmd(t.Context())
 
 	for _, name := range []string{
 		"list",