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/config/concierge/config.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 concierge contains functionality to load/store Config's from/to
@@ -8,7 +8,7 @@ package concierge
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"strings"
 
 	"k8s.io/utils/pointer"
@@ -43,7 +43,7 @@ const (
 // This function will decode that base64-encoded data to PEM bytes to be stored
 // in the Config.
 func FromPath(ctx context.Context, path string) (*Config, error) {
-	data, err := ioutil.ReadFile(path)
+	data, err := os.ReadFile(path)
 	if err != nil {
 		return nil, fmt.Errorf("read file: %w", err)
 	}

internal/config/concierge/config_test.go

@@ -1,11 +1,10 @@
-// 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 concierge
 
 import (
 	"context"
-	"io/ioutil"
 	"os"
 	"testing"
 
@@ -585,7 +584,7 @@ func TestFromPath(t *testing.T) {
 			// this is a serial test because it sets the global logger
 
 			// Write yaml to temp file
-			f, err := ioutil.TempFile("", "pinniped-test-config-yaml-*")
+			f, err := os.CreateTemp("", "pinniped-test-config-yaml-*")
 			require.NoError(t, err)
 			defer func() {
 				err := os.Remove(f.Name())