build: only check --engine-strict for production deps (#455)

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Source-Link: googleapis/synthtool@5451633

packages/google-cloud-texttospeech/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/nodejs-text-to-speech.git",
-        "sha": "8c43bf3ca8ecdc51ec032afe8e8b60fa7ab5faca"
+        "sha": "ccbf8e8712aaed6b2fac2644c3b35a5b62da7f32"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "0c868d49b8e05bc1f299bc773df9eb4ef9ed96e9"
+        "sha": "5451633881133e5573cc271a18e73b18caca8b1b"
       }
     }
   ],