fix dangling reference warning, also skip CBC installation on macos-11, package installation fails because of the old macos version

Author: patrickbr

.github/workflows/build.yml

@@ -207,7 +207,7 @@ jobs:
       - name: Checkout submodules
         run: git submodule update --init --recursive
       - name: install dependencies
-        run: brew install --force --overwrite cmake && brew install --force --overwrite glpk && brew tap coin-or-tools/coinor && brew install --force --overwrite coin-or-tools/coinor/cbc
+        run: brew install --force --overwrite cmake && brew install --force --overwrite glpk 
       - name: cmake
         run: mkdir build && cd build && cmake ..
       - name: make

src/loom/optim/OptGraph.cpp

@@ -674,7 +674,7 @@ size_t OptGraph::getNumLines() const {
   for (auto n : getNds()) {
     for (auto e : n->getAdjList()) {
       if (e->getFrom() != n) continue;
-      for (const auto& to : getFirstLnEdgPart(e).lnEdg->pl().getLines()) {
+      for (auto to : getFirstLnEdgPart(e).lnEdg->pl().getLines()) {
         lines.insert(to.line);
       }
     }