Hack CI to build SouraVX repo branch pubnames_flang

Instead of master.

.github/workflows/flang-tests.yml

@@ -76,7 +76,7 @@ jobs:
       - name: Checkout flang
         run: |
           cd ../..
-          git clone --depth 1 --single-branch --branch master https://github.com/flang-compiler/flang.git
+          git clone --depth 1 --single-branch --branch pubnames_flang https://github.com/SouraVX/flang.git
           cd flang
           mkdir -p build && cd build