Update dependency google-api-core to v1.26.0

Author: renovate-bot

requirements.txt

@@ -2,7 +2,7 @@ cachetools==4.2.1
 certifi==2020.6.20
 cffi==1.14.2
 chardet==4.0.0
-google-api-core==1.22.1
+google-api-core==1.26.0
 google-auth==1.25.0
 google-cloud-bigquery==2.7.0
 google-cloud-core==1.4.1