[ci] Try clang 15 for clang-sanitisers job

.github/workflows/main.yml

@@ -184,6 +184,7 @@ jobs:
       run: |
         sudo apt-get update
         sudo apt-get install \
+            clang-15 \
             gettext \
             libwxgtk3.0-gtk3-dev \
             libavcodec-dev \
@@ -210,8 +211,8 @@ jobs:
       run: |
         # We use clang here because (at least currently) it supports a few
         # extra sanitiser checks compared to GCC.
-        export CC='ccache clang'
-        export CXX='ccache clang++'
+        export CC='ccache clang-15'
+        export CXX='ccache clang++-15'
         # float-divide-by-zero, nullability and unsigned-overflow aren't
         # undefined behaviour checks, but they catch for things we don't expect
         # our code to do.