chore: add pre-commit-config to renovate ignore paths (#552)

Disable renovate PRs on the .pre-commit-config.yaml which is templated from synthtool. https://docs.renovatebot.com/configuration-options/#ignorepaths

Source-Author: Bu Sun Kim <8822365+busunkim96@users.noreply.github.com>
Source-Date: Mon Mar 15 09:05:39 2021 -0600
Source-Repo: googleapis/synthtool
Source-Sha: 2c54c473779ea731128cea61a3a6c975a08a5378
Source-Link: googleapis/synthtool@2c54c47

renovate.json

@@ -1,5 +1,6 @@
 {
   "extends": [
     "config:base",  ":preserveSemverRanges"
-  ]
+  ],
+  "ignorePaths": [".pre-commit-config.yaml"]
 }

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/python-bigquery.git",
-        "sha": "f0259eb7ed4ff254ee238e87651992ff93481dae"
+        "sha": "efdf1c653770f7c03c17e31e3c2f279bb685637b"
       }
     },
     {
@@ -19,14 +19,14 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "4dca4132c6d63788c6675e1b1e11e7b9225f8694"
+        "sha": "2c54c473779ea731128cea61a3a6c975a08a5378"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "4dca4132c6d63788c6675e1b1e11e7b9225f8694"
+        "sha": "2c54c473779ea731128cea61a3a6c975a08a5378"
       }
     }
   ],