chore(deps): update dependency gcp-releasetool to v1.16.0 (main) (#351)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| gcp-releasetool | `==1.14.0` -> `==1.16.0` | [![age](https://developer.mend.io/api/mc/badges/age/pypi/gcp-releasetool/1.16.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/pypi/gcp-releasetool/1.16.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/pypi/gcp-releasetool/1.14.0/1.16.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/gcp-releasetool/1.14.0/1.16.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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.kokoro/requirements.txt

@@ -134,9 +134,9 @@ cryptography==41.0.3 \
     #   -r requirements.txt
     #   gcp-releasetool
     #   secretstorage
-gcp-releasetool==1.14.0 \
-    --hash=sha256:a39708206838477bf42804a9dd7b549131ff3fc08c6abb0dd6939e274bd6dfd4 \
-    --hash=sha256:aa163ec8322045c9d46e03f8f7500974568bd5d8d322b6a2d492068a5bdf57bf
+gcp-releasetool==1.16.0 \
+    --hash=sha256:27bf19d2e87aaa884096ff941aa3c592c482be3d6a2bfe6f06afafa6af2353e3 \
+    --hash=sha256:a316b197a543fd036209d0caba7a8eb4d236d8e65381c80cbc6d7efaa7606d63
     # via -r requirements.txt
 google-auth==2.22.0 \
     --hash=sha256:164cba9af4e6e4e40c3a4f90a1a6c12ee56f14c0b4868d1ca91b32826ab334ce \