Upgrade the linter and fix all new linter warnings

Also fix some tests that were broken by bumping golang and dependencies
in the previous commits.

Note that in addition to changes made to satisfy the linter which do not
impact the behavior of the code, this commit also adds ReadHeaderTimeout
to all usages of http.Server to satisfy the linter (and because it
seemed like a good suggestion).

internal/controller/authenticator/webhookcachefiller/webhookcachefiller.go

@@ -1,4 +1,4 @@
-// Copyright 2020-2021 the Pinniped contributors. All Rights Reserved.
+// Copyright 2020-2022 the Pinniped contributors. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
 // Package webhookcachefiller implements a controller for filling an authncache.Cache with each added/updated WebhookAuthenticator.
@@ -6,7 +6,6 @@ package webhookcachefiller
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 
 	"github.com/go-logr/logr"
@@ -64,7 +63,7 @@ func (c *controller) Sync(ctx controllerlib.Context) error {
 		return fmt.Errorf("failed to get WebhookAuthenticator %s/%s: %w", ctx.Key.Namespace, ctx.Key.Name, err)
 	}
 
-	webhookAuthenticator, err := newWebhookAuthenticator(&obj.Spec, ioutil.TempFile, clientcmd.WriteToFile)
+	webhookAuthenticator, err := newWebhookAuthenticator(&obj.Spec, os.CreateTemp, clientcmd.WriteToFile)
 	if err != nil {
 		return fmt.Errorf("failed to build webhook config: %w", err)
 	}