chore(deps): update dependency google-api-core to v2.26.0

Author: renovate-bot

.kokoro/docs/docker/requirements.txt

@@ -28,9 +28,9 @@ gcp-docuploader==0.7.2 \
     --hash=sha256:3916d2b46239a2d86ba9427a7f21e3762f21c1e1d34e4f066317a9765e43c90c \
     --hash=sha256:aaa7ef9d2ecc3cd03fa284977a68772e03ca4b0cbd8ae3cc85a745dc57fad25e
     # via -r requirements.in
-google-api-core==2.25.2 \
-    --hash=sha256:1c63aa6af0d0d5e37966f157a77f9396d820fba59f9e43e9415bc3dc5baff300 \
-    --hash=sha256:e9a8f62d363dc8424a8497f4c2a47d6bcda6c16514c935629c257ab5d10210e7
+google-api-core==2.26.0 \
+    --hash=sha256:2b204bd0da2c81f918e3582c48458e24c11771f987f6258e6e227212af78f3ed \
+    --hash=sha256:e6e6d78bd6cf757f4aee41dcc85b07f485fbb069d5daa3afb126defba1e91a62
     # via
     #   google-cloud-core
     #   google-cloud-storage