ci: removing linkage-monitor from the required checks (#234)

Source-Author: Tomo Suzuki <suztomo@google.com>
Source-Date: Wed Aug 25 13:18:10 2021 -0400
Source-Repo: googleapis/synthtool
Source-Sha: e2aa5bcc3356d9e3b8b53de3b5c86226447d3a22
Source-Link: googleapis/synthtool@e2aa5bc

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-accesscontextmanager.git",
-        "sha": "524627c5da5a535292beb81288bcbc805ab59d65"
+        "sha": "24afe3283762c2f0708c68109121bc6fb537021f"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "63cff634aabb85854caa511c5837ea6b45f42b4b"
+        "sha": "e2aa5bcc3356d9e3b8b53de3b5c86226447d3a22"
       }
     }
   ],