revert: ♻ Revert Rust toolchain to 1.88.0 (revert PR #362) (#392)

Revert #362, back to Rust toolchain v1.88.0, as the newer version causes
an issue in the runtime release publishing flow.

.github/workflows/task-check-licenses.yml

@@ -14,7 +14,7 @@ jobs:
       - name: Install Rust toolchain
         uses: actions-rs/toolchain@v1
         with:
-          toolchain: 1.90.0
+          toolchain: 1.88.0
           override: true
       - name: Verify Licenses
         working-directory: operator

operator/rust-toolchain.toml

@@ -1,5 +1,5 @@
 [toolchain]
-channel = "1.90.0"
+channel = "1.88.0"
 components = [
     "cargo",
     "clippy",