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_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