chore: bump toolchain to v4.28.0-rc1 (#352)

Author: kim-em

lake-manifest.json

@@ -5,7 +5,7 @@
    "type": "git",
    "subDir": null,
    "scope": "",
-   "rev": "55c37290ff6186e2e965d68cf853a57c0702db82",
+   "rev": "28e0856d4424863a85b18f38868c5420c55f9bae",
    "name": "Cli",
    "manifestFile": "lake-manifest.json",
    "inputRev": "main",
@@ -15,7 +15,7 @@
    "type": "git",
    "subDir": null,
    "scope": "",
-   "rev": "b09d573cbacf5a8e767292e0edeec787a81689ce",
+   "rev": "8668e1ab7c987fb8ed1349f14c3b7b60bd5f27b6",
    "name": "UnicodeBasic",
    "manifestFile": "lake-manifest.json",
    "inputRev": "main",
@@ -25,7 +25,7 @@
    "type": "git",
    "subDir": null,
    "scope": "",
-   "rev": "c8a6a4dae7c7f42949a1058427a75c20447e990f",
+   "rev": "1c5c543d2637aebf90c80aead2d401ae88db13cc",
    "name": "BibtexQuery",
    "manifestFile": "lake-manifest.json",
    "inputRev": "master",

lean-toolchain

@@ -1 +1 @@
-leanprover/lean4:v4.27.0
+leanprover/lean4:v4.28.0-rc1