Try switching to Xcode 15.4 osx15 cling ci job

Author: mcbarton

.github/workflows/ci.yml

@@ -299,6 +299,7 @@ jobs:
                 brew install llvm@15
                 brew remove llvm@18
                 brew cleanup
+                xcode-select -s /Applications/Xcode_15.4.app
                 echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
                 echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV
             else
@@ -781,6 +782,7 @@ jobs:
                 brew install llvm@15
                 brew remove llvm@18
                 brew cleanup
+                xcode-select -s /Applications/Xcode_15.4.app
                 echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
                 echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV
             else