Move to clang-format 15 (#621)

The current version requires clang-format-9.  This now getting hard to get.
This commit moves it to the clang-format-15, which is the latest in 22.04.

Also, updates clang-tidy to 15 as well.

.github/workflows/main.yml

@@ -400,12 +400,14 @@ jobs:
 
   # Job to run clang-format and report errors
   format:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     # We don't need to do the build for this job, but we need to configure it to get the clang-format target
     steps:
     - uses: actions/checkout@v3
     - name: Install clang-tidy and clang-format
-      run: sudo apt install clang-tidy-9 clang-format-9
+      run: |
+        sudo apt update
+        sudo apt install clang-tidy-15 clang-format-15
     - name: Configure CMake
       run: cmake -B ${{github.workspace}}/build -DSNMALLOC_USE_CXX17=ON
     # Run the clang-format check and error if it generates a diff
@@ -417,7 +419,7 @@ jobs:
         git diff --exit-code
     - name: Run clang-tidy
       run: |
-        clang-tidy-9  src/snmalloc/override/malloc.cc  -header-filter="`pwd`/*" -warnings-as-errors='*' -export-fixes=tidy.fail -- -std=c++17 -mcx16 -DSNMALLOC_PLATFORM_HAS_GETENTROPY=0
+        clang-tidy-15  src/snmalloc/override/malloc.cc  -header-filter="`pwd`/*" -warnings-as-errors='*' -export-fixes=tidy.fail -- -std=c++17 -mcx16 -DSNMALLOC_PLATFORM_HAS_GETENTROPY=0
         if [ -f tidy.fail ] ; then
           cat tidy.fail
           exit 1