Github runner: Upgrade LLVM to LLVM 16

Recent github runner config changes for Windows breaks use of LLVM 15
and does not install LLVM 16 in the image.

This change adds an LLVM upgrade step that should pull in LLVM 16. This
follows scikit-image/scikit-image#7109.

Bug: actions/runner-images#812

.github/workflows/test.yml

@@ -29,7 +29,7 @@ jobs:
         uses: actions/cache@v3
         with:
           path: ~/bazel-disk-cache
-          key: bazel-disk-cache-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('.bazelversion', '.bazelrc', 'WORKSPACE') }}
+          key: bazel-disk-cache-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('.bazelversion', '.bazelrc', 'WORKSPACE', '.github/workflows/test.yml') }}
           # Use an older cache key, if available.
           restore-keys: |
             bazel-disk-cache-${{ runner.os }}-${{ runner.arch }}-
@@ -57,8 +57,10 @@ jobs:
         # bazel generates huge amounts of debug information on Windows which slows down the build
         # and takes up an excessive amount of cache space.
         run: |
+            bazelisk clean --expunge
             [System.IO.File]::WriteAllLines((Join-Path -Path $env:USERPROFILE -ChildPath '.bazelrc'), 'startup --output_user_root=C:/tmp')
             [System.IO.File]::WriteAllLines((Join-Path -Path $env:USERPROFILE -ChildPath '.bazelrc'), 'build:windows --config=windows_no_dbg')
+            choco upgrade llvm
       - name: Bazel build
         # timestamps are no longer being added here, the GitHub logs include timestamps (Use
         # 'Show timestamps' on the web interface)