Update Rust toolchain version to 1.88.0

Rather than direct upgrade from 1.87 to 1.90 (as its causing test failures)

Considering gradual migration hence just bumping to 1.88

Author: akhileshb

rust-toolchain.toml

@@ -1,5 +1,5 @@
 [toolchain]
-channel = "1.90.0"
+channel = "1.88.0"
 profile = "minimal"
 components = ["rustfmt", "clippy"]
 targets = [