Bump Fuchsia toolchain for testing

This updates the Fuchsia SDK used to test rust on Fuchsia to
26.20241211.7.1, and clang to the development version 20 from
388d7f144880dcd85ff31f06793304405a9f44b6.

Author: Steven Grady

src/ci/docker/scripts/build-fuchsia-toolchain.sh

@@ -4,13 +4,13 @@ set -ex
 source shared.sh
 
 FUCHSIA_SDK_URL=https://chrome-infra-packages.appspot.com/dl/fuchsia/sdk/core/linux-amd64
-FUCHSIA_SDK_ID=version:21.20240610.2.1
-FUCHSIA_SDK_SHA256=2d2d057fc3f0404197cced2200f88cbcdaaf5fbf6475955045091f8676791ce7
+FUCHSIA_SDK_ID=version:26.20241211.7.1
+FUCHSIA_SDK_SHA256=2cb7a9a0419f7413a46e0ccef7dad89f7c9979940d7c1ee87fac70ff499757d6
 FUCHSIA_SDK_USR_DIR=/usr/local/core-linux-amd64-fuchsia-sdk
 CLANG_DOWNLOAD_URL=\
 https://chrome-infra-packages.appspot.com/dl/fuchsia/third_party/clang/linux-amd64
-CLANG_DOWNLOAD_ID=git_revision:3809e20afc68d7d03821f0ec59b928dcf9befbf4
-CLANG_DOWNLOAD_SHA256=3c2c442b61cd9e8f1b567738f6d53cffe11b3fc820e7dae87a82a0859be8f204
+CLANG_DOWNLOAD_ID=git_revision:388d7f144880dcd85ff31f06793304405a9f44b6
+CLANG_DOWNLOAD_SHA256=970d1f427b9c9a3049d8622c80c86830ff31b5334ad8da47a2f1e81143197e8b
 
 install_clang() {
   mkdir -p clang_download