bootstrapper: ignore "journald" not in $PATH in constructor

In unit tests, NewCollector may be called on systems that do not have
"journalctl" in $PATH.
We can defer checking if the command can work by not checking cmd.Err in
the constructor.

bootstrapper/internal/journald/journald.go

@@ -30,9 +30,6 @@ type Collector struct {
 // NewCollector creates a new Collector for journald logs.
 func NewCollector(ctx context.Context) (*Collector, error) {
 	cmd := exec.CommandContext(ctx, "journalctl")
-	if cmd.Err != nil {
-		return nil, cmd.Err
-	}
 	stdoutPipe, err := cmd.StdoutPipe()
 	if err != nil {
 		return nil, err