fix: fail if no stages were found (#1970)

* fix: fail if no stages were found

Adds a warning message if act is cannot find any stages to run
with the filters provided.

Reproduction:
- run `act -j gibberish`

Desired behavior: some indication I did something silly
Actual behavior: no output, just exit with success.

As a human who often makes spelling mistakes,
it would be nice if act warned me what I was doing that was silly
rather than exiting apparently doing
nothing with no obvious indication
I did something wrong.

* Revert "fix: fail if no stages were found"

This reverts commit 226adf1c15cf4c01d516a05dc923507e6999978d.

* fix: fail if no stages were found

Errors if no stages were found with the given filters.
Prints out a helpful error message, pointing users
in the right place for how to specify which stage to run.

Reproduction:
- run `act -j gibberish`

Desired behavior: some indication I did something silly
Actual behavior: no output, just exit with success.

As a human who often makes spelling mistakes,
it would be nice if act warned me what I was doing that was silly
rather than exiting apparently doing
nothing with no obvious indication
I did something wrong.

act/model/planner_test.go

@@ -39,3 +39,25 @@ func TestPlanner(t *testing.T) {
 		}
 	}
 }
+
+func TestWorkflow(t *testing.T) {
+	log.SetLevel(log.DebugLevel)
+
+	workflow := Workflow{
+		Jobs: map[string]*Job{
+			"valid_job": {
+				Name: "valid_job",
+			},
+		},
+	}
+
+	// Check that an invalid job id returns error
+	result, err := createStages(&workflow, "invalid_job_id")
+	assert.NotNil(t, err)
+	assert.Nil(t, result)
+
+	// Check that an valid job id returns non-error
+	result, err = createStages(&workflow, "valid_job")
+	assert.Nil(t, err)
+	assert.NotNil(t, result)
+}