treewide: errors variables should be prefixed with Err

Change-Id: Ic277f98ebcd03356500ce7daba199738e701e81c
Reviewed-on: https://review.monogon.dev/c/monogon/+/3025
Tested-by: Jenkins CI
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Vouch-Run-CI: Tim Windelschmidt <tim@monogon.tech>
diff --git a/cloud/shepherd/provider/equinix/provider.go b/cloud/shepherd/provider/equinix/provider.go
index f642eaf..1752349 100644
--- a/cloud/shepherd/provider/equinix/provider.go
+++ b/cloud/shepherd/provider/equinix/provider.go
@@ -292,7 +292,7 @@
 			return &k, nil
 		}
 	}
-	return nil, NoSuchKey
+	return nil, ErrNoSuchKey
 }
 
 // sshEquinixId looks up the Equinix key identified by providerConfig.KeyLabel,
@@ -344,7 +344,7 @@
 func (ep *equinixProvider) SSHEquinixEnsure(ctx context.Context) error {
 	k, err := ep.sshEquinix(ctx)
 	switch {
-	case errors.Is(err, NoSuchKey):
+	case errors.Is(err, ErrNoSuchKey):
 		if err := ep.sshEquinixUpload(ctx); err != nil {
 			return fmt.Errorf("while uploading key: %w", err)
 		}
diff --git a/cloud/shepherd/provider/equinix/provider_config.go b/cloud/shepherd/provider/equinix/provider_config.go
index be3bc27..b54488f 100644
--- a/cloud/shepherd/provider/equinix/provider_config.go
+++ b/cloud/shepherd/provider/equinix/provider_config.go
@@ -12,7 +12,7 @@
 )
 
 var (
-	NoSuchKey = errors.New("no such key")
+	ErrNoSuchKey = errors.New("no such key")
 )
 
 // providerConfig contains configuration options used by both the Initializer and