tests/kokoro: use gcc 13 instead of gcc 9

Change-Id: I17eca5434f62e6c375d91f3223bec113c008201a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/74828
Reviewed-by: Shahbaz Youssefi <syoussefi@google.com>
Tested-by: Shahbaz Youssefi <syoussefi@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@google.com>

tests/kokoro/gcp_ubuntu/docker.sh

diff --git a/tests/kokoro/gcp_ubuntu/docker.sh b/tests/kokoro/gcp_ubuntu/docker.sh
index 0e27b3a..b69d5da 100755
--- a/tests/kokoro/gcp_ubuntu/docker.sh
+++ b/tests/kokoro/gcp_ubuntu/docker.sh
@@ -44,7 +44,7 @@
 . /bin/using.sh # Declare the bash `using` function for configuring toolchains.
 
 using cmake-3.31.2
-using gcc-9
+using gcc-13
 
 status "Cloning to clean source directory at '${SRC_DIR}'"