Fix errcheck warnings

Signed-off-by: z1cheng <imchench@gmail.com>

internal/net/dns/dns_test.go

@@ -40,13 +40,16 @@ func TestGetDNSServers(t *testing.T) {
 	defer f.Close()
 	defer os.Remove(f.Name())
 
-	os.WriteFile(f.Name(), []byte(`
+	err = os.WriteFile(f.Name(), []byte(`
 	# comment
 	; comment
 	nameserver 2001:4860:4860::8844
 	nameserver 2001:4860:4860::8888
 	nameserver 8.8.8.8
 	`), file.ReadWriteByUser)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
 
 	defResolvConf = f.Name()
 	s, err = GetSystemNameServers()

internal/net/ssl/ssl_test.go

@@ -397,7 +397,9 @@ func newFakeCertificate(t *testing.T) ([]byte, string, string) {
 		t.Errorf("failed to write test key: %v", err)
 	}
 
-	certFile.Write(cert)
+	if _, err := certFile.Write(cert); err != nil {
+		t.Errorf("failed to write cert: %v", err)
+	}
 	defer certFile.Close()
 
 	keyFile, err := os.CreateTemp("", "key-")
@@ -405,7 +407,9 @@ func newFakeCertificate(t *testing.T) ([]byte, string, string) {
 		t.Errorf("failed to write test key: %v", err)
 	}
 
-	keyFile.Write(key)
+	if _, err := keyFile.Write(key); err != nil {
+		t.Errorf("failed to write key: %v", err)
+	}
 	defer keyFile.Close()
 
 	return cert, certFile.Name(), keyFile.Name()