Bump net-smtp from 0.3.3 to 0.4.0

Bumps [net-smtp](https://github.com/ruby/net-smtp) from 0.3.3 to 0.4.0.
- [Release notes](https://github.com/ruby/net-smtp/releases)
- [Changelog](https://github.com/ruby/net-smtp/blob/master/NEWS.md)
- [Commits](https://github.com/ruby/net-smtp/compare/v0.3.3...v0.4.0)

---
updated-dependencies:
- dependency-name: net-smtp
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -269,7 +269,7 @@ GEM
       net-protocol
     net-protocol (0.2.1)
       timeout
-    net-smtp (0.3.3)
+    net-smtp (0.4.0)
       net-protocol
     nio4r (2.5.9)
     nokogiri (1.15.4)