treewide: replace error comparisons and assertions with errors.Is

Change-Id: Id2424eb155f2c6842c72c5fafd124d428ef901f2
Reviewed-on: https://review.monogon.dev/c/monogon/+/2994
Tested-by: Jenkins CI
Reviewed-by: Serge Bazanski <serge@monogon.tech>
diff --git a/metropolis/pkg/kmod/manager.go b/metropolis/pkg/kmod/manager.go
index 1630a7f..3b3f875 100644
--- a/metropolis/pkg/kmod/manager.go
+++ b/metropolis/pkg/kmod/manager.go
@@ -2,6 +2,7 @@
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -150,7 +151,7 @@
 	}
 	defer module.Close()
 	err = LoadModule(module, "", 0)
-	if err != nil && err != unix.EEXIST {
+	if err != nil && errors.Is(err, unix.EEXIST) {
 		return fmt.Errorf("error loading kernel module %v: %w", modMeta.Name, err)
 	}
 	s.loadedModules[modIdx] = true