deps: update dependency urllib3 to v1.26.15 (#1596)

Author: renovate-bot

.kokoro/requirements.txt

@@ -392,9 +392,9 @@ typing-extensions==4.1.1 \
     --hash=sha256:1a9462dcc3347a79b1f1c0271fbe79e844580bb598bafa1ed208b94da3cdcd42 \
     --hash=sha256:21c85e0fe4b9a155d0799430b0ad741cdce7e359660ccbd8b530613e8df88ce2
     # via -r .kokoro/requirements.in
-urllib3==1.26.12 \
-    --hash=sha256:3fa96cf423e6987997fc326ae8df396db2a8b7c667747d47ddd8ecba91f4a74e \
-    --hash=sha256:b930dd878d5a8afb066a637fbb35144fe7901e3b209d1cd4f524bd0e9deee997
+urllib3==1.26.15 \
+    --hash=sha256:8a388717b9476f934a21484e8c8e61875ab60644d29b9b39e11e4b9dc1c6b305 \
+    --hash=sha256:aa751d169e23c7479ce47a0cb0da579e3ede798f994f5816a74e4f4500dcea42
     # via requests
 zipp==3.6.0 \
     --hash=sha256:71c644c5369f4a6e07636f0aa966270449561fcea2e3d6747b8d23efaa9d7832 \