Skip this performance regression test.

The test measures things on the order of 20ms.  On a loaded machine, we
have seen enough variation that the test would fail.

--- grep-2.22/tests/long-pattern-perf	2016-01-03 12:52:38.491575007 +0100
+++ grep-2.22/tests/long-pattern-perf	2016-01-03 12:53:39.768464687 +0100
@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+exit 77
 . "${srcdir=.}/init.sh"; path_prepend_ ../src
 
 fail=0
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span title='2023-06-14 14:52:21 +0300'>2023-06-14</span></td><td><a href='/guix/commit/gnu/system/images?id=f3114ac4f0f1ac20a85dcb20c44cb32e06c22a14'>system: images: Add unmatched module.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
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<tr><td><span title='2022-09-24 14:49:09 +0200'>2022-09-24</span></td><td><a href='/guix/commit/gnu/system/images?id=c8112f3bd95269ce4aca12dedbfe61bb6b37acae'>system: images: Add wsl2 module.</a><span class='msg-avail'>...</span></td><td>Alex Griffin</td></tr>
<tr><td><span title='2022-09-24 14:49:07 +0200'>2022-09-24</span></td><td><a href='/guix/commit/gnu/system/images?id=08a7eb187f09aeefbb03b8b28b0d67aab33d4a06'>platforms: x86: Rename Hurd hurd to i586-gnu.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2022-09-24 14:20:36 +0200'>2022-09-24</span></td><td><a href='/guix/commit/gnu/system/images?id=c009c286a23f48b56731c3e7bc4875a9e88857c4'>image: Make the operating-system field mandatory.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
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<tr><td><span title='2022-05-25 14:47:36 +0300'>2022-05-25</span></td><td><a href='/guix/commit/gnu/system/images?id=be43625159de560b651d3a744db5b79b4f1fe55f'>images: hurd: Adjust module imports.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2022-05-25 09:27:25 +0200'>2022-05-25</span></td><td><a href='/guix/commit/gnu/system/images?id=dab819d5c4c55609efae098c8e3c2f2757c34e5b'>Move (gnu platform) and (gnu platforms ...) to guix/.</a><span class='msg-avail'>...</span></td><td>Josselin Poiret</td></tr>
<tr><td><span title='2022-03-15 13:14:29 +0100'>2022-03-15</span></td><td><a href='/guix/commit/gnu/system/images?id=2543cb485479d29700ac14762875db084b90ed54'>images: novena: Fix build.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2021-10-18 10:00:50 +0200'>2021-10-18</span></td><td><a href='/guix/commit/gnu/system/images?id=f513afa37f2760c7f842883598302795c896fc75'>system: image: Ensure Hurd images are cross-compiled if needed.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-10-11 12:05:39 +0000'>2021-10-11</span></td><td><a href='/guix/commit/gnu/system/images?id=d5073fd113c621fe0b55382f7dd336ee118e759f'>gnu: Add platform support.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2021-08-29 01:05:26 -0400'>2021-08-29</span></td><td><a href='/guix/commit/gnu/system/images?id=da4e40948326387d5bcda58783914d5f9ce8b095'>Migrate to the new 'targets' field of bootloader-configuration.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-08-28 17:47:12 +0200'>2021-08-28</span></td><td><a href='/guix/commit/gnu/system/images?id=1dbed7e0988842b8fe8189b7a7e64ff72f72cd61'>images: pinebook-pro: Fix the agetty baud rate.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>