build: only check --engine-strict for production deps (#518)

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Source-Link: googleapis/synthtool@5451633

packages/google-cloud-language/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/nodejs-language.git",
-        "sha": "1007cafe7140594a1a831f27387b7a83fb96f847"
+        "sha": "eda55b8a371ec0e8b025e6d44a77da4c3d27db22"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "0c868d49b8e05bc1f299bc773df9eb4ef9ed96e9"
+        "sha": "5451633881133e5573cc271a18e73b18caca8b1b"
       }
     }
   ],