WIP: (Unrelated to ticket per se) Seems gcc-13 is no longer pre-insta…

…lled in this Ubuntu. Might be related to move of `latest` to newer Ubuntu and different pre-installed compilers there... though we are not using `latest`. Details TBD; for now setting install=true for that one; hopefully it will install and the gcc-13 tests will start passing again.

.github/workflows/main.yml

@@ -213,6 +213,7 @@ jobs:
     if: |
       needs.setup.outputs.proceed-else-not == 'true'
 
+    # XXX gcc-13
     strategy:
       fail-fast: false
       matrix:
@@ -237,6 +238,7 @@ jobs:
             version: 13
             c-path: /usr/bin/gcc-13
             cpp-path: /usr/bin/g++-13
+            install: True
           - id: clang-13
             name: clang
             version: 13