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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<div class='path'>path: <a href='/guix/log/?id=691178d67b91a0150ed1dd0e3540441cecc83e61'>root</a>/<a href='/guix/log/tests?id=691178d67b91a0150ed1dd0e3540441cecc83e61'>tests</a>/<a href='/guix/log/tests/inferior.scm?id=691178d67b91a0150ed1dd0e3540441cecc83e61'>inferior.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/inferior.scm?id=691178d67b91a0150ed1dd0e3540441cecc83e61&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-01-21 00:14:38 +0100'>2021-01-21</span></td><td><a href='/guix/commit/tests/inferior.scm?id=98d3abe7440717724263cacca8c36e9f43d53fcc'>repl: Fix exception handling for interpreted code.</a><span class='msg-avail'>...<span class='msg-tooltip'>The 'stack' variable could be #f when code is interpreted, which in
practice happens when running in "legacy" mode--i.e., when
'open-inferior' invokes "guile" instead of "guix repl".

* guix/repl.scm (send-repl-response)[handle-exception]: Check whether
STACK is true before passing it to 'stack-&gt;frames'.
* tests/inferior.scm ("&amp;inferior-exception, legacy mode"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-01-21 00:14:38 +0100'>2021-01-21</span></td><td><a href='/guix/commit/tests/inferior.scm?id=074a201c33f822a7ab59512e7ee8b301204ff732'>inferior: Add 'inferior-eval-with-store' tests.</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/inferior.scm ("inferior-eval-with-store, exception")
("inferior-eval-with-store, not a procedure"): New tests.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-21 22:16:02 +0100'>2020-03-21</span></td><td><a href='/guix/commit/tests/inferior.scm?id=d19b14c8349ce8cacb62619ab68953265daeeca7'>Merge branch 'master' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-03-19 15:14:08 +0100'>2020-03-19</span></td><td><a href='/guix/commit/tests/inferior.scm?id=1dca6aaafa9f842565deab1fe7e6929f25544551'>inferior: '&amp;inferior-exception' includes a stack trace.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/inferior.scm (port-&gt;inferior): Bump protocol to (0 1 1).
(&amp;inferior-exception)[stack]: New field.
(read-repl-response): Recognize 'exception' form for protocol (0 1 1).
* tests/inferior.scm ("&amp;inferior-exception"): Check the value returned
by 'inferior-exception-stack'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-17 15:46:15 +0100'>2020-03-17</span></td><td><a href='/guix/commit/tests/inferior.scm?id=9d0c2c6e5226bbd11e710bd4efa8f25e9ffb5a86'>tests: Fix up reference to 'guile-2.2'.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to b6bee63bed4f013064c0d902e7c8b83ed7514ade.

* tests/inferior.scm ("inferior-package-search-paths"): Refer to
'guile-3.0' instead of 'guile-2.2'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-12 11:52:38 +0100'>2020-03-12</span></td><td><a href='/guix/commit/tests/inferior.scm?id=f7537e30b892cef09d91902547c00e5fa9b66f3b'>inferior: Distinguish inferior exceptions.</a><span class='msg-avail'>...<span class='msg-tooltip'>This avoids ambiguities when looking at a backtrace where the exception
was actually thrown by an inferior in a very different context.

* guix/inferior.scm (&amp;inferior-exception): New condition type.
(read-repl-response): Add optional 'inferior' parameter.  Raise
'&amp;inferior-exception' instead of rethrowing to KEY when receiving an
'exception' message.
(read-inferior-response): Pass INFERIOR to 'read-repl-response'.
* tests/inferior.scm ("&amp;inferior-exception"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>