Use containers for clang libc++ w/wo ubsan

Author: igaztanaga

.github/workflows/ci.yml

@@ -342,7 +342,8 @@ jobs:
           - toolset: clang
             compiler: clang++-15
             cxxstd: "03,11,14,17,20,2b"
-            os: ubuntu-22.04
+            os: ubuntu-latest
+            container: ubuntu:22.04
             install:
               - clang-15
               - libc++-15-dev
@@ -353,7 +354,8 @@ jobs:
           - toolset: clang
             compiler: clang++-18
             cxxstd: "11,14,17,20,2b"
-            os: ubuntu-24.04
+            os: ubuntu-latest
+            container: ubuntu:24.04
             install:
               - clang-18
               - libc++-18-dev
@@ -364,7 +366,8 @@ jobs:
           - toolset: clang
             compiler: clang++-18
             cxxstd: "11,14,17,20,23,2c"
-            os: ubuntu-24.04
+            os: ubuntu-latest
+            container: ubuntu:24.04
             install:
               - clang-20
               - libc++-20-dev
@@ -379,7 +382,8 @@ jobs:
             cxxflags: -pipe -stdlib=libc++
             linkflags: -stdlib=libc++
             ubsan: 1
-            os: ubuntu-22.04
+            os: ubuntu-latest
+            container: ubuntu:22.04
             install:
               - clang-14
               - libc++-14-dev
@@ -392,7 +396,8 @@ jobs:
             cxxflags: -pipe -stdlib=libc++
             linkflags: -stdlib=libc++
             ubsan: 1
-            os: ubuntu-24.04
+            os: ubuntu-latest
+            container: ubuntu:24.04
             install:
               - clang-18
               - libc++-18-dev
@@ -405,7 +410,8 @@ jobs:
             cxxflags: -pipe -stdlib=libc++
             linkflags: -stdlib=libc++
             ubsan: 1
-            os: ubuntu-26.04
+            os: ubuntu-latest
+            container: ubuntu:26.04
             install:
               - clang-20
               - libc++-20-dev