tests: stty: add require_controlling_input_terminal_ to bad-speed test

tests: stty: add require_controlling_input_terminal_ to bad-speed test

The bad-speed test runs 'stty ispeed 9600' without a --file argument,
which requires a controlling terminal. Without it, stty fails early with
'Inappropriate ioctl for device' before reaching cfsetispeed, causing
the test to skip with a misleading 'LD_PRELOAD interception failed'
message.

* tests/stty/bad-speed.sh: Add require_controlling_input_terminal_
to match the other stty tests (stty.sh, stty-pairs.sh, stty-row-col.sh,
stty-invalid.sh) which all require a controlling terminal.
From https://github.com/coreutils/coreutils/pull/160