[ghactions] Always build against respective TRIQS branch

Author: Wentzell

.github/workflows/build.yml

@@ -104,7 +104,7 @@ jobs:
         CC: ${{ matrix.cc }}
         CXX: ${{ matrix.cxx }}
       run: |
-        git clone https://github.com/TRIQS/triqs --branch unstable
+        git clone https://github.com/TRIQS/triqs --branch ${{ github.ref_name }}
         mkdir triqs/build && cd triqs/build
         cmake .. -DBuild_Tests=OFF -DCMAKE_INSTALL_PREFIX=$HOME/install
         make -j1 install VERBOSE=1