Use old conan version for old CentOS 7

Author: garyo

.github/workflows/build.yml

@@ -41,7 +41,8 @@ jobs:
             need_node20_vol: true
             has_cmake_presets: false
             buildtype: Release
-            conan_version: 2.20.1
+            # use old conan version for CentOS 7
+            conan_version: 2.15.0
             cxx-standard: 17
             cxx-compiler: clang++
             cc-compiler: clang
@@ -58,7 +59,8 @@ jobs:
             need_node20_vol: true
             has_cmake_presets: false
             buildtype: Release
-            conan_version: 2.20.1
+            # use old conan version for CentOS 7
+            conan_version: 2.15.0
             cxx-standard: 17
             cxx-compiler: clang++
             cc-compiler: clang