bump webpush-go to release version

vendor/github.com/ergochat/webpush-go/v2/CHANGELOG.md

@@ -1,7 +1,7 @@
 # Changelog
 All notable changes to webpush-go will be documented in this file.
 
-## [2.0.0] - 2025-01-01
+## [2.0.0] - 2025-01-16
 
 * Update the `Keys` struct definition to store `Auth` as `[16]byte` and `P256dh` as `*ecdh.PublicKey`
     * `Keys` can no longer be compared with `==`; use `(*Keys.Equal)` instead

vendor/github.com/ergochat/webpush-go/v2/README.md

@@ -4,7 +4,7 @@
 
 Web Push API Encryption with VAPID support.
 
-This library is a fork of [SherClockHolmes/webpush-go](https://github.com/SherClockHolmes/webpush-go).
+This library is a fork of [SherClockHolmes/webpush-go](https://github.com/SherClockHolmes/webpush-go). See CHANGELOG.md for details on migrating from the upstream library.
 
 ```bash
 go get -u github.com/ergochat/webpush-go/v2

vendor/github.com/ergochat/webpush-go/v2/webpush.go

@@ -29,7 +29,7 @@ var (
 
 	invalidAuthKeyLength = errors.New("invalid auth key length (must be 16)")
 
-	defaultHTTPClient = &http.Client{}
+	defaultHTTPClient HTTPClient = &http.Client{}
 )
 
 // HTTPClient is an interface for sending the notification HTTP request / testing