rust-toolchain: Bump toolchain version to 1.69.0

which, compared to the previous 1.67.0, has the following impacts on
`zellij`:

- [Turn off debuginfo for build deps][2]: Increases build time (on my
  machine) from ~230 s in 1.67.0 to ~250 s now, *which is unexpected*

This version also changes [handling of the `default-features` flag][3]
when specifying dependencies in `Cargo.toml`. If a dependent crate
requires `default-features = true` on a crate that is required as
`default-features = false` further up the dependency tree, the `true`
setting "wins". We only specify `default-features = false` for three
crates total:

- `names`: This is used only by us
- `surf`: This is used only by us
- `vte`: This is also required by `strip-ansi-escapes`, but that has
  `default-features = false` as well

How this affects our transitive dependencies is unknown at this point.

[2]: rust-lang/cargo#11252
[3]: rust-lang/cargo#11409

rust-toolchain.toml

@@ -1,5 +1,5 @@
 # This file is updated by `update-toolchain.sh`
 [toolchain]
-channel = "1.75.0"
+channel = "1.69.0"
 components = ["rustfmt", "clippy", "rust-analysis"]
 targets = ["wasm32-wasi", "x86_64-unknown-linux-musl"]