Kokoro: Update gcc and doxygen toolchains

Change-Id: I73c1dc13dd695c6e2e6c935d0a9acc62eef0bc5c
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/109120
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>

kokoro/linux/docker.sh

diff --git a/kokoro/linux/docker.sh b/kokoro/linux/docker.sh
index 9663d39..bea2fd9 100755
--- a/kokoro/linux/docker.sh
+++ b/kokoro/linux/docker.sh
@@ -75,7 +75,7 @@
 . /bin/using.sh # Declare the bash `using` function for configuring toolchains.
 
 using depot_tools
-using doxygen-1.8.18
+using doxygen-1.9.5
 
 status "Creating source directory '${SRC_DIR}' and build directory '${BUILD_DIR}'"
 mkdir -p ${SRC_DIR}
@@ -105,7 +105,7 @@
         COMMON_CMAKE_FLAGS+=" -DTINT_BUILD_AST_FUZZER=1"
         COMMON_CMAKE_FLAGS+=" -DTINT_BUILD_REGEX_FUZZER=1"
     elif [ "$BUILD_TOOLCHAIN" == "gcc" ]; then
-        using gcc-9
+        using gcc-10
     fi
 
     if [ "$BUILD_SANITIZER" == "asan" ]; then