fix(renovate): regex pattern for rust-toolchain.toml (#676)

Author: ReenigneArcher

renovate-config.json5

@@ -108,7 +108,7 @@
       "customType": "regex",
       "managerFilePatterns": ["/(^|\/)rust-toolchain.toml$/"],
       "matchStrings": [
-        "(?:^|\\r?\\n)channel[ \\t]*=[ \\t]*\"(?<currentValue>[^\"\\r\\n]+)\"[ \\t]*(?=$|\\r?\\n)",
+        "channel[ \\t]*=[ \\t]*\"(?<currentValue>[^\"\\r\\n]+)\"",
       ],
       "datasourceTemplate": "github-tags",
       "depNameTemplate": "rust-lang/rust",