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/test/util/runners.go b/metropolis/test/util/runners.go
index 99de4f1..a34c070 100644
--- a/metropolis/test/util/runners.go
+++ b/metropolis/test/util/runners.go
@@ -30,7 +30,7 @@
 				launch.Log("Test: %s: okay after %.1f seconds", name, time.Since(start).Seconds())
 				return
 			}
-			if err == ctx.Err() {
+			if errors.Is(err, ctx.Err()) {
 				t.Fatal(lastErr)
 			}
 			if errors.Is(err, &PermanentError{}) {