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>

federationapi/statistics/statistics.go

@@ -5,10 +5,10 @@ import (
 	"math"
 	"math/rand"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/sirupsen/logrus"
-	"go.uber.org/atomic"
 
 	"github.com/matrix-org/dendrite/federationapi/storage"
 	"github.com/matrix-org/gomatrixserverlib/spec"
@@ -169,7 +169,7 @@ func (s *ServerStatistics) Success(method SendMethod) {
 	// NOTE : Sending to the final destination vs. a relay server has
 	// slightly different semantics.
 	if method == SendDirect {
-		s.successCounter.Inc()
+		s.successCounter.Add(1)
 		if s.blacklisted.Load() && s.statistics.DB != nil {
 			if err := s.statistics.DB.RemoveServerFromBlacklist(s.serverName); err != nil {
 				logrus.WithError(err).Errorf("Failed to remove %q from blacklist", s.serverName)
@@ -195,7 +195,7 @@ func (s *ServerStatistics) Failure() (time.Time, bool) {
 	// start a goroutine which will wait out the backoff and
 	// unset the backoffStarted flag when done.
 	if s.backoffStarted.CompareAndSwap(false, true) {
-		backoffCount := s.backoffCount.Inc()
+		backoffCount := s.backoffCount.Add(1)
 
 		if backoffCount >= s.statistics.FailuresUntilAssumedOffline {
 			s.assumedOffline.CompareAndSwap(false, true)