ci: fix broken Mac CI with full path to compiler (#2096)

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

.github/workflows/ci.yml

@@ -528,8 +528,8 @@ jobs:
           - desc: MacOS-15-Intel aclang17/C++17/py3.13 llvm18 oiio-release
             runner: macos-15-intel
             nametag: macos15
-            cc_compiler: clang
-            cxx_compiler: clang++
+            cc_compiler: /usr/bin/clang
+            cxx_compiler: /usr/bin/clang++
             cxx_std: 17
             openimageio_ver: dev-3.0
             python_ver: "3.13"
@@ -540,25 +540,25 @@ jobs:
           - desc: MacOS-14-ARM llvm19 oiio-release
             runner: macos-14
             nametag: macos14-arm
-            cc_compiler: clang
-            cxx_compiler: clang++
+            cc_compiler: /usr/bin/clang
+            cxx_compiler: /usr/bin/clang++
             cxx_std: 17
             openimageio_ver: main
             python_ver: "3.13"
             setenvs: export LLVMBREWVER="@19"
           - desc: MacOS-15-ARM aclang16/C++17/py3.13 llvm21 oiio-main
             runner: macos-15
             nametag: macos15-arm
-            cc_compiler: clang
-            cxx_compiler: clang++
+            cc_compiler: /usr/bin/clang
+            cxx_compiler: /usr/bin/clang++
             cxx_std: 17
             python_ver: "3.13"
             openimageio_ver: main
           - desc: MacOS-26-ARM aclang16/C++17/py3.14 llvm21 oiio-main
             runner: macos-26
             nametag: macos26-arm
-            cc_compiler: clang
-            cxx_compiler: clang++
+            cc_compiler: /usr/bin/clang
+            cxx_compiler: /usr/bin/clang++
             cxx_std: 17
             python_ver: "3.14"
             openimageio_ver: main