treewide: add nolint exceptions for returnerrcheck

Change-Id: Ife7e28de0317627994cb55d6bd5b10fa6016332b
Reviewed-on: https://review.monogon.dev/c/monogon/+/2997
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/node/core/localstorage/crypt/blockdev.go b/metropolis/node/core/localstorage/crypt/blockdev.go
index fb55aab..d021d9c 100644
--- a/metropolis/node/core/localstorage/crypt/blockdev.go
+++ b/metropolis/node/core/localstorage/crypt/blockdev.go
@@ -111,6 +111,7 @@
 
 	table, err := gpt.Read(blkdev)
 	if err != nil {
+		//nolint:returnerrcheck
 		return nil // Probably just not a GPT-partitioned disk
 	}
 
diff --git a/metropolis/node/core/network/dhcp4c/transport/transport_unicast.go b/metropolis/node/core/network/dhcp4c/transport/transport_unicast.go
index e142f3b..0876a82 100644
--- a/metropolis/node/core/network/dhcp4c/transport/transport_unicast.go
+++ b/metropolis/node/core/network/dhcp4c/transport/transport_unicast.go
@@ -114,6 +114,7 @@
 	err := t.udpConn.Close()
 	t.udpConn = nil
 	if err != nil && errors.Is(err, net.ErrClosed) {
+		//nolint:returnerrcheck
 		return nil
 	}
 	return err
diff --git a/metropolis/node/core/rpc/server_authentication.go b/metropolis/node/core/rpc/server_authentication.go
index 516883a..f847126 100644
--- a/metropolis/node/core/rpc/server_authentication.go
+++ b/metropolis/node/core/rpc/server_authentication.go
@@ -206,6 +206,7 @@
 		if err := cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature); err != nil {
 			// Peer presented a certificate that is not self-signed - for example a user or
 			// node certificate. Ignore it.
+			//nolint:returnerrcheck
 			return &res, nil
 		}
 		res.Unauthenticated.SelfSignedPublicKey = cert.PublicKey.(ed25519.PublicKey)
diff --git a/metropolis/node/kubernetes/plugins/kvmdevice/kvmdevice.go b/metropolis/node/kubernetes/plugins/kvmdevice/kvmdevice.go
index 902803b..bef049a 100644
--- a/metropolis/node/kubernetes/plugins/kvmdevice/kvmdevice.go
+++ b/metropolis/node/kubernetes/plugins/kvmdevice/kvmdevice.go
@@ -153,6 +153,7 @@
 		k.logger.Warning("KVM is not available. Check firmware settings and CPU.")
 		supervisor.Signal(ctx, supervisor.SignalHealthy)
 		supervisor.Signal(ctx, supervisor.SignalDone)
+		//nolint:returnerrcheck
 		return nil
 	}