t/lib-gpg: quote path to ${GNUPGHOME}/trustlist.txt

t/lib-gpg: quote path to ${GNUPGHOME}/trustlist.txt

When gpgsm is installed, lib-gpg.sh attempts to update trustlist.txt to
relax the checking of some root certificate requirements.  The path to
"${GNUPGHOME}" contains spaces which cause an "ambiguous redirect"
warning when bash is used to run the tests:

  $ bash t7030-verify-tag.sh
  /git/t/lib-gpg.sh: line 66: ${GNUPGHOME}/trustlist.txt: ambiguous redirect
  ok 1 - create signed tags
  ok 2 # skip create signed tags x509  (missing GPGSM)
  ...

No warning is issued when using bash called as /bin/sh, dash, or mksh.

Quote the path to ensure the redirect works as intended and sets the
GPGSM prereq.  While we're here, drop the space after ">>".

Signed-off-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>