Take advantage of changes in recent Go versions (#3361)

Given that #2714 wasn't merged but we are now at a minimum supported Go
version of 1.20 (soon to be 1.21), I wanted to carry over some of the
changes. Namely:
- Fix the log typo
- Simplify build constraints for unix
- Use stdlib atomic package

### Pull Request Checklist

<!-- Please read
https://matrix-org.github.io/dendrite/development/contributing before
submitting your pull request -->

* [x] I have added Go unit tests or [Complement integration
tests](https://github.com/matrix-org/complement) for this PR _or_ I have
justified why this PR doesn't need tests
* [x] Pull request includes a [sign off below using a legally
identifiable
name](https://matrix-org.github.io/dendrite/development/contributing#sign-off)
_or_ I have already signed off privately

Signed-off-by: `0x1a8510f2 <admin@0x1a8510f2.space>`

---------

Co-authored-by: devonh <devon.dmytro@gmail.com>

cmd/dendrite-demo-pinecone/relay/retriever.go

@@ -17,13 +17,13 @@ package relay
 import (
 	"context"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	federationAPI "github.com/matrix-org/dendrite/federationapi/api"
 	relayServerAPI "github.com/matrix-org/dendrite/relayapi/api"
 	"github.com/matrix-org/gomatrixserverlib/spec"
 	"github.com/sirupsen/logrus"
-	"go.uber.org/atomic"
 )
 
 const (
@@ -54,7 +54,7 @@ func NewRelayServerRetriever(
 		federationAPI:       federationAPI,
 		relayAPI:            relayAPI,
 		relayServersQueried: make(map[spec.ServerName]bool),
-		running:             *atomic.NewBool(false),
+		running:             atomic.Bool{},
 		quit:                quit,
 	}
 }