Pin the stable version to whatever the latest CI image contains!

Byron · Byron · commit b1e97770490a · 2025-10-02T18:07:29.000+02:00
Otherwise builds will once again take longer (but we also can
keep using our caches longer).
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
@@ -1,5 +1,6 @@
 [toolchain]
-channel = "stable"
+# IMPORTANT: This should match CI so it won't download the toolchain all the time.
+channel = "1.90"
 components = [
     "rustfmt",
     "clippy",
