test: avoid leaking goroutines

This commit adds a test that checks for goroutine
leaks in the `workerpool` package, and also fixes
two goroutine leaks.

There is unfortunately no easy way of running
`goleak` before every test without either a lot of
copy-paste, or additional code to ensure every
test file has a `TestMain` function.

A leaked goroutine will produce the following
error with `goleak`:

```
goleak: Errors on successful test run: found
unexpected goroutines: [Goroutine 7 in state chan
receive, with
github.com/nlnwa/warchaeology/internal/workerpool
.New.func1 on top of the stack: goroutine 7 [chan
receive]:
github.com/nlnwa/warchaeology/internal/workerpool.
New.func1(0xc00008a1e0)
./warchaeology/internal/workerpool/workerpool.go:
23
+0x66 created by
github.com/nlnwa/warchaeology/internal/workerpool.New
in goroutine 6
./warchaeology/internal/workerpool/workerpool.go:
22
+0x85 ] FAIL
github.com/nlnwa/warchaeology/internal/workerpool
0.450s FAIL
```

go.mod

@@ -20,6 +20,7 @@ require (
 	github.com/spf13/pflag v1.0.5
 	github.com/spf13/viper v1.18.2
 	github.com/stretchr/testify v1.9.0
+	go.uber.org/goleak v1.2.0
 )
 
 require (

internal/workerpool/workerpool_test.go

@@ -5,17 +5,24 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"go.uber.org/goleak"
 )
 
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}
+
 func TestCreatePool(t *testing.T) {
 	ctx := context.Background()
 	pool := New(ctx, 1)
+	defer pool.CloseWait()
 	assert.NotNil(t, pool)
 }
 
 func TestSubmitJob(t *testing.T) {
 	ctx := context.Background()
 	pool := New(ctx, 1)
+	defer pool.CloseWait()
 	assert.NotNil(t, pool)
 
 	pool.Submit(func() {})