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/run/runner_test.go

@@ -47,7 +47,7 @@ func TestRunnerCapabilitiesAndDeclare(t *testing.T) {
 	})).Return(connect.NewResponse(&runnerv1.DeclareResponse{}), nil)
 
 	r := &Runner{client: cli}
-	_, err := r.Declare(context.Background(), []string{"ubuntu"})
+	_, err := r.Declare(t.Context(), []string{"ubuntu"})
 	require.NoError(t, err)
 }