build(deps): bump certifi from 2024.6.2 to 2024.7.4 in /.kokoro

Bumps [certifi](https://github.com/certifi/python-certifi) from 2024.6.2 to 2024.7.4.
- [Commits](certifi/python-certifi@2024.06.02...2024.07.04)

---
updated-dependencies:
- dependency-name: certifi
  dependency-type: indirect
...

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

.kokoro/requirements.txt

@@ -20,9 +20,9 @@ cachetools==5.3.3 \
     --hash=sha256:0abad1021d3f8325b2fc1d2e9c8b9c9d57b04c3932657a72465447332c24d945 \
     --hash=sha256:ba29e2dfa0b8b556606f097407ed1aa62080ee108ab0dc5ec9d6a723a007d105
     # via google-auth
-certifi==2024.6.2 \
-    --hash=sha256:3cd43f1c6fa7dedc5899d69d3ad0398fd018ad1a17fba83ddaf78aa46c747516 \
-    --hash=sha256:ddc6c8ce995e6987e7faf5e3f1b02b302836a0e5d98ece18392cb1a36c72ad56
+certifi==2024.7.4 \
+    --hash=sha256:5a1e7645bc0ec61a09e26c36f6106dd4cf40c6db3a1fb6352b0244e7fb057c7b \
+    --hash=sha256:c198e21b1289c2ab85ee4e67bb4b4ef3ead0892059901a8d5b622f24a1101e90
     # via requests
 cffi==1.16.0 \
     --hash=sha256:0c9ef6ff37e974b73c25eecc13952c55bceed9112be2d9d938ded8e856138bcc \