chore(deps): bump urllib3 from 1.26.19 to 2.6.3 in /.kokoro

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.19 to 2.6.3.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.19...2.6.3)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-version: 2.6.3
  dependency-type: indirect
...

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

Author: dependabot[bot]

.kokoro/requirements.txt

@@ -502,9 +502,9 @@ typing-extensions==4.10.0 \
     --hash=sha256:69b1a937c3a517342112fb4c6df7e72fc39a38e7891a5730ed4985b5214b5475 \
     --hash=sha256:b0abd7c89e8fb96f98db18d86106ff1d90ab692004eb746cf6eda2682f91b3cb
     # via -r requirements.in
-urllib3==1.26.19 \
-    --hash=sha256:37a0344459b199fce0e80b0d3569837ec6b6937435c5244e7fd73fa6006830f3 \
-    --hash=sha256:3e3d753a8618b86d7de333b4223005f68720bcd6a7d2bcb9fbd2229ec7c1e429
+urllib3==2.6.3 \
+    --hash=sha256:1b62b6884944a57dbe321509ab94fd4d3b307075e0c2eae991ac71ee15ad38ed \
+    --hash=sha256:bf272323e553dfb2e87d9bfd225ca7b0f467b919d7bbd355436d3fd37cb0acd4
     # via
     #   requests
     #   twine