build(java): readme.sh should be executable (#267)

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Source-Link: googleapis/synthtool@0762e8e

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-datalabeling.git",
-        "sha": "c14b87a9a53fb3a9149166bd99a16752c9cac702"
+        "sha": "7de51927dbb05edf84d9dcb6ff58984d31a0840e"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "8a7a3021fe97aa0a3641db642fe2b767f1c8110f"
+        "sha": "0762e8ee2ec21cdfc4d82020b985a104feb0453b"
       }
     }
   ],