The debuginfo test harness does not load pretty-printers for windows-gnu

[saethlin]

As part of #128913 I am moving one of our pretty-printing tests from cdb-only to ignore-windows-gnu, because based on what I'm seeing in try-jobs, the pretty-printers are not loaded on windows-gnu targets. I do not know why that is the case.

We are doing some path escaping when setting up with gdb, I do not know if that is related:

rust/src/tools/compiletest/src/runtest.rs

Lines 1019 to 1022 in 9cb1998

	script_str.push_str(&format!(
	"add-auto-load-safe-path {}\n",
	rust_pp_module_abs_path.replace(r"\", r"\\")
	));

This is probably related to #29658