[lldb] the SwiftREPL/BreakpointSimple.test has been flaking on linux for weeks

[finagolfin]

We see it repeatedly timing out on 6.4 and trunk runs of the various linux snapshot toolchain CI:

06:56:40  TIMEOUT: lldb-shell :: SwiftREPL/BreakpointSimple.test (615 of 615)
06:56:40 
 ******************** TEST 'lldb-shell :: SwiftREPL/BreakpointSimple.test' FAILED ********************
06:56:40  Exit Code: -9
06:56:40  Timeout: Reached timeout of 600 seconds