[lldb] fix failing diagnostics test when Unicode is supported (llvm#172038)

This patch fixes a test failure introduced by
llvm#171832 due to a check which
was not properly updated.

(cherry picked from commit 8515dda)

Author: charles-zablit

lldb/test/Shell/Commands/command-expr-diagnostics.test

@@ -24,7 +24,7 @@
 # RUN: "expression -- FOO(\"\")" 2>&1 | FileCheck %s --check-prefix=CHECK4
 #            (lldb) expression -- FOO("")
 # CHECK4:{{^                     (\^|˄)}}
-# CHECK4: {{^                     note: in instantiation of function template}}
+# CHECK4: {{^                     (╰─ )?note: in instantiation of function template}}
 # CHECK4: error: <user expression
 
 # RUN: echo expression --\na\n+\nb