adios2: update test

Needed for #233787.

Author: carlocab

Formula/a/adios2.rb

@@ -102,7 +102,7 @@ def install
 
   test do
     adios2_config_flags = Utils.safe_popen_read(bin/"adios2-config", "--cxx").chomp.split
-    system "mpic++", pkgshare/"test/bpWriter.cpp", *adios2_config_flags
+    system "mpic++", "-std=c++17", pkgshare/"test/bpWriter.cpp", *adios2_config_flags
     system "./a.out"
     assert_path_exists testpath/"myVector_cpp.bp"