`Test Libs 1.88.0` 从未在 1.88.0 上运行: ci.yml:306 硬编码了 `stable` (与 #2106/#2116 相同的问题)

The test-libs matrix declares toolchain: ["1.88.0", "stable"], but ci.yml:306 literally installs toolchain: stable. matrix.toolchain appears nowhere else in the job except its name, so Test Libs 1.88.0 and Test Libs stable are the same job run twice. In the latest run on main (33879050611, all 35 jobs green), the Test Libs 1.88.0 job installs stable and reports rustc 1.98.1; the string 1.88 occurs exactly once in its 4101-line log, on the job-name line. test-libs is in the required gate's needs:, so that green is load-bearing. This is the same defect as #2106 and #2116 ("the ... CI jobs were unintentionally using the stable toolchain from Rust-toolchain.toml instead of the matrix-specified toolchain"), both merged a year ago. test-libs is the third matrix-toolchain job in the file and the only one that got neither half — and it needs both, since Rust-toolchain.toml pins channel = "stable" and overrides rustup default inside the tree: