build(deps): bump server_sent_event_stage from 1.2.0 to 1.2.1

Bumps [server_sent_event_stage](https://github.com/mbta/server_sent_event_stage) from 1.2.0 to 1.2.1.
- [Release notes](https://github.com/mbta/server_sent_event_stage/releases)
- [Changelog](https://github.com/mbta/server_sent_event_stage/blob/main/CHANGELOG.md)
- [Commits](mbta/server_sent_event_stage@v1.2.0...v1.2.1)

---
updated-dependencies:
- dependency-name: server_sent_event_stage
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

mix.lock

@@ -65,7 +65,7 @@
   "retry": {:hex, :retry, "0.18.0", "dc58ebe22c95aa00bc2459f9e0c5400e6005541cf8539925af0aa027dc860543", [:mix], [], "hexpm", "9483959cc7bf69c9e576d9dfb2b678b71c045d3e6f39ab7c9aa1489df4492d73"},
   "screens_config": {:git, "https://github.com/mbta/screens-config-lib.git", "25fb47c58fc0b485c8c6df78fe94914292856903", [ref: "25fb47c58fc0b485c8c6df78fe94914292856903"]},
   "sentry": {:hex, :sentry, "10.6.2", "a867ab728d424e187ccb2bccc388170a740a79bc0ddccabd72d303b203acbe0e", [:mix], [{:hackney, "~> 1.8", [hex: :hackney, repo: "hexpm", optional: true]}, {:jason, "~> 1.1", [hex: :jason, repo: "hexpm", optional: true]}, {:nimble_options, "~> 1.0", [hex: :nimble_options, repo: "hexpm", optional: false]}, {:nimble_ownership, "~> 0.3.0", [hex: :nimble_ownership, repo: "hexpm", optional: false]}, {:phoenix, "~> 1.6", [hex: :phoenix, repo: "hexpm", optional: true]}, {:phoenix_live_view, "~> 0.20", [hex: :phoenix_live_view, repo: "hexpm", optional: true]}, {:plug, "~> 1.6", [hex: :plug, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: true]}], "hexpm", "31bb84247274f9262fd300df0e3eb73302e4849cc6b7a6560bb2465f03fbd446"},
-  "server_sent_event_stage": {:hex, :server_sent_event_stage, "1.2.0", "3baa30e046714880e8cf0155db0820ad1b32bdd00ee7e94332167f91bf4891c3", [:mix], [{:castore, "~> 0.1", [hex: :castore, repo: "hexpm", optional: true]}, {:ex_doc, "~> 0.22", [hex: :ex_doc, repo: "hexpm", optional: true]}, {:gen_stage, "~> 1.1", [hex: :gen_stage, repo: "hexpm", optional: false]}, {:mint, "~> 1.4", [hex: :mint, repo: "hexpm", optional: false]}], "hexpm", "8c886ee46c3a63f0f1df48a0d3392fd996741dd3ba000b828d0ebcfbf1ccb264"},
+  "server_sent_event_stage": {:hex, :server_sent_event_stage, "1.2.1", "ede8c63496e19f039972503aa242cb4c16a301d495be7d9fdda2f952298cbf0c", [:mix], [{:castore, "~> 0.1.0 or ~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:ex_doc, "~> 0.22", [hex: :ex_doc, repo: "hexpm", optional: true]}, {:gen_stage, "~> 1.1", [hex: :gen_stage, repo: "hexpm", optional: false]}, {:mint, "~> 1.4", [hex: :mint, repo: "hexpm", optional: false]}], "hexpm", "5b84b2c886bfa3ab38143d424eff6ec9d224e65ca576652aab762ed9d11847c3"},
   "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.7", "354c321cf377240c7b8716899e182ce4890c5938111a1296add3ec74cf1715df", [:make, :mix, :rebar3], [], "hexpm", "fe4c190e8f37401d30167c8c405eda19469f34577987c76dde613e838bbc67f8"},
   "stream_data": {:hex, :stream_data, "1.1.1", "fd515ca95619cca83ba08b20f5e814aaf1e5ebff114659dc9731f966c9226246", [:mix], [], "hexpm", "45d0cd46bd06738463fd53f22b70042dbb58c384bb99ef4e7576e7bb7d3b8c8c"},
   "sweet_xml": {:hex, :sweet_xml, "0.7.4", "a8b7e1ce7ecd775c7e8a65d501bc2cd933bff3a9c41ab763f5105688ef485d08", [:mix], [], "hexpm", "e7c4b0bdbf460c928234951def54fe87edf1a170f6896675443279e2dbeba167"},