dim: tag once, try 2

Tag just once to avoid the old tag left on the local machine with
possibly the wrong message. Even more importantly: the revert of first
version was correct, but at least with my current git version (2.44) it
doesn't work. The second call to git-tag to amend the commit message
will also move the tag to another commit:

	+ git tag -F- drm-xe-fixes-2024-04-18-1 'drm-xe-fixes@{upstream}'
	+ '[' git == git ']'
	+ key_arg=-s
	+ git tag -s -f drm-xe-fixes-2024-04-18-1
	Updated tag 'drm-xe-fixes-2024-04-18-1' (was 46d02aa1b02c)

So, even if it showed the correct log in gitk and updated the message,
it ended up tagging the wrong commit.  We could add "$branch@{upstream}"
in the second invocation, but I think this also highlight another
shortcoming of calling git-tag twice.

In this "try 2" to avoid the breakage from v1 with some editors, do not
pass the summary as stdin to `git-tag`, but rather create a tmp file.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>