chore(deps): bump protobuf from 4.25.3 to 4.25.8 in /.kokoro

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 4.25.3 to 4.25.8.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/protobuf_release.bzl)
- [Commits](protocolbuffers/protobuf@v4.25.3...v4.25.8)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-version: 4.25.8
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.kokoro/requirements.txt

@@ -397,18 +397,18 @@ platformdirs==3.11.0 \
     --hash=sha256:cf8ee52a3afdb965072dcc652433e0c7e3e40cf5ea1477cd4b3b1d2eb75495b3 \
     --hash=sha256:e9d171d00af68be50e9202731309c4e658fd8bc76f55c11c7dd760d023bda68e
     # via virtualenv
-protobuf==4.25.3 \
-    --hash=sha256:19b270aeaa0099f16d3ca02628546b8baefe2955bbe23224aaf856134eccf1e4 \
-    --hash=sha256:209ba4cc916bab46f64e56b85b090607a676f66b473e6b762e6f1d9d591eb2e8 \
-    --hash=sha256:25b5d0b42fd000320bd7830b349e3b696435f3b329810427a6bcce6a5492cc5c \
-    --hash=sha256:7c8daa26095f82482307bc717364e7c13f4f1c99659be82890dcfc215194554d \
-    --hash=sha256:c053062984e61144385022e53678fbded7aea14ebb3e0305ae3592fb219ccfa4 \
-    --hash=sha256:d4198877797a83cbfe9bffa3803602bbe1625dc30d8a097365dbc762e5790faa \
-    --hash=sha256:e3c97a1555fd6388f857770ff8b9703083de6bf1f9274a002a332d65fbb56c8c \
-    --hash=sha256:e7cb0ae90dd83727f0c0718634ed56837bfeeee29a5f82a7514c03ee1364c019 \
-    --hash=sha256:f0700d54bcf45424477e46a9f0944155b46fb0639d69728739c0e47bab83f2b9 \
-    --hash=sha256:f1279ab38ecbfae7e456a108c5c0681e4956d5b1090027c1de0f934dfdb4b35c \
-    --hash=sha256:f4f118245c4a087776e0a8408be33cf09f6c547442c00395fbfb116fac2f8ac2
+protobuf==4.25.8 \
+    --hash=sha256:077ff8badf2acf8bc474406706ad890466274191a48d0abd3bd6987107c9cde5 \
+    --hash=sha256:15a0af558aa3b13efef102ae6e4f3efac06f1eea11afb3a57db2901447d9fb59 \
+    --hash=sha256:27d498ffd1f21fb81d987a041c32d07857d1d107909f5134ba3350e1ce80a4af \
+    --hash=sha256:504435d831565f7cfac9f0714440028907f1975e4bed228e58e72ecfff58a1e0 \
+    --hash=sha256:6135cf8affe1fc6f76cced2641e4ea8d3e59518d1f24ae41ba97bcad82d397cd \
+    --hash=sha256:83e6e54e93d2b696a92cad6e6efc924f3850f82b52e1563778dfab8b355101b0 \
+    --hash=sha256:9ad7ef62d92baf5a8654fbb88dac7fa5594cfa70fd3440488a5ca3bfc6d795a7 \
+    --hash=sha256:bd551eb1fe1d7e92c1af1d75bdfa572eff1ab0e5bf1736716814cdccdb2360f9 \
+    --hash=sha256:ca809b42f4444f144f2115c4c1a747b9a404d590f18f37e9402422033e464e0f \
+    --hash=sha256:d552c53d0415449c8d17ced5c341caba0d89dbf433698e1436c8fa0aae7808a3 \
+    --hash=sha256:f4510b93a3bec6eba8fd8f1093e9d7fb0d4a24d1a81377c10c0e5bbfe9e4ed24
     # via
     #   gcp-docuploader
     #   gcp-releasetool