deps: Update dependency gcp-releasetool to v1.16.0 (#1479)

Author: renovate-bot

.kokoro/requirements.txt

@@ -128,9 +128,9 @@ gcp-docuploader==0.6.5 \
     --hash=sha256:30221d4ac3e5a2b9c69aa52fdbef68cc3f27d0e6d0d90e220fc024584b8d2318 \
     --hash=sha256:b7458ef93f605b9d46a4bf3a8dc1755dad1f31d030c8679edf304e343b347eea
     # via -r requirements.in
-gcp-releasetool==1.10.5 \
-    --hash=sha256:174b7b102d704b254f2a26a3eda2c684fd3543320ec239baf771542a2e58e109 \
-    --hash=sha256:e29d29927fe2ca493105a82958c6873bb2b90d503acac56be2c229e74de0eec9
+gcp-releasetool==1.16.0 \
+    --hash=sha256:27bf19d2e87aaa884096ff941aa3c592c482be3d6a2bfe6f06afafa6af2353e3 \
+    --hash=sha256:a316b197a543fd036209d0caba7a8eb4d236d8e65381c80cbc6d7efaa7606d63
     # via -r requirements.in
 google-api-core==2.8.2 \
     --hash=sha256:06f7244c640322b508b125903bb5701bebabce8832f85aba9335ec00b3d02edc \