roachtest: fix parameters passed to require.NoError

When context is passed to an assertion, the parameters *must* be a
string format, followed by arguments (as you would in a call to
`fmt.Sprintf`). The previous code would panic trying to cast int to
string.

Informs #95416

Release note: None

pkg/cmd/roachtest/tests/multitenant_distsql.go

@@ -139,7 +139,7 @@ func runMultiTenantDistSQL(
 				default:
 					// procede to report error
 				}
-				require.NoError(t, err, li, iter)
+				require.NoError(t, err, "instance idx = %d, iter = %d", li, iter)
 				iter++
 			}
 		})