fix: Bump MSRV from 1.91 to 1.92 (#124)

Author: github-actions[bot]

.github/variables/rust-versions.env

@@ -1 +1 @@
-target=1.91
+target=1.92

eventsource-client/Cargo.toml

@@ -5,7 +5,7 @@ description = "Client for the Server-Sent Events protocol (aka EventSource)"
 repository = "https://github.com/launchdarkly/rust-eventsource-client"
 authors = ["LaunchDarkly"]
 edition = "2021"
-rust-version = "1.91.0"
+rust-version = "1.92.0"
 license = "Apache-2.0"
 keywords = ["launchdarkly", "feature-flags", "feature-toggles", "eventsource", "server-sent-events"]
 exclude = ["CHANGELOG.md"]