tests: stabilize `test-split-legacy-inline-changelog.t` on Windows
The `tar` command is unable to process "C:\path\to\foo.tar" style paths, which
is how `$TESTDIR` is constructed. It also didn't work with
`$TESTDIR_FORWARD_SLASH`- both failed with:
tar: Cannot connect to C: resolve failed
[128]
But `cat` can handle it if the path is quoted, and `tar` can read from stdin.
#require emacs
$ emacs -q -no-site-file -batch -l $TESTDIR/../contrib/hg-test-mode.el \
> -f ert-run-tests-batch-and-exit
Running 1 tests (*) (glob)
passed 1/1 hg-test-mode--compilation-mode-support* (glob)
Ran 1 tests, 1 results as expected* (glob)