all: replace non-trivial uses of package ioutil with os (#24886)

Co-authored-by: Martin Holst Swende <martin@swende.se>

cmd/geth/accountcmd_test.go

@@ -17,7 +17,6 @@
 package main
 
 import (
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -163,7 +162,7 @@ Password: {{.InputLine "foo"}}
 Address: {d4584b5f6229b7be90727b0fc8c6b91bb427821f}
 `)
 
-	files, err := ioutil.ReadDir(filepath.Join(geth.Datadir, "keystore"))
+	files, err := os.ReadDir(filepath.Join(geth.Datadir, "keystore"))
 	if len(files) != 1 {
 		t.Errorf("expected one key file in keystore directory, found %d files (error: %v)", len(files), err)
 	}

cmd/geth/version_check_test.go

@@ -19,7 +19,6 @@ package main
 import (
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -55,7 +54,7 @@ func testVerification(t *testing.T, pubkey, sigdir string) {
 		t.Fatal(err)
 	}
 	// Signatures, with and without comments, both trusted and untrusted
-	files, err := ioutil.ReadDir(sigdir)
+	files, err := os.ReadDir(sigdir)
 	if err != nil {
 		t.Fatal(err)
 	}