[PR gdb/27026] CTRL-C is ignored when debug info is downloaded

[PR gdb/27026] CTRL-C is ignored when debug info is downloaded

During debuginfod downloads, ctrl-c should result in the download
being cancelled and skipped.  However in some cases, ctrl-c fails to
get delivered to gdb during downloading.  This can result in downloads
being unskippable.

Fix this by ensuring that target_terminal::ours is in effect for the
duration of each download.

Co-authored-by: Tom de Vries <tdevries@suse.de>
https://sourceware.org/bugzilla/show_bug.cgi?id=27026#c3