[lldb][test] Fix cast dropping const warnin in TestBreakpointSetCallback.cpp

When building with gcc I get this warning:
```
<...>TestBreakpointSetCallback.cpp:58:25: warning: cast from type ‘const char*’ to type ‘void*’ casts away qualifiers [-Wcast-qual]
   58 |   void *baton = (void *)"hello";
      |                         ^~~~~~~
```

Use the address of a mutable global variable instead. All we care about
is that the address passed as the baton is the same one we get later.

0 files changed, 0 insertions, 0 deletions