ci: Add '-specs' to ccache ignore option list

`-specs=` is an alternate form of `--specs=`, which is now used by the
Zephyr build system.

This commit adds `-specs=*` to the ccache ignore option list because, as
with `--specs=*`, ccache is unable to resolve the toolchain specs file path
and refuses to cache when this option is specified.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>