Suppress a warning from grep which causes tests to fail.

Taken from upstream pull request:

  https://github.com/aureliojargas/clitest/pull/54

diff --git a/test/inline-match-egrep.sh b/test/inline-match-egrep.sh
--- a/test/inline-match-egrep.sh
+++ b/test/inline-match-egrep.sh
@@ -42,7 +42,7 @@ $ printf ' \t  \t\t   \n'       #=> --egrep ^ 	  		   $
 # egrep regexes. You'll need to test in your system if that's the
 # case. I recommend using a literal tab to avoid problems.
 
-$ printf 'may\tfail'            #=> --egrep ^may\tfail$
+$ printf 'may\tfail'            #=> --egrep ^may\\tfail$
 $ printf 'may\tfail'            #=> --egrep ^may[\t]fail$
 $ printf 'will\tmatch'          #=> --egrep ^will	match$
 
@@ -51,7 +51,7 @@ $ printf 'will\tmatch'          #=> --egrep ^will	match$
 # These tests will fail:
 
 $ printf 'will\nfail'           #=> --egrep will.*fail
-$ printf 'will\nfail'           #=> --egrep will\nfail
+$ printf 'will\nfail'           #=> --egrep will\\nfail
 
 # If one line of a multiline results matches, the test is OK
 
'/guix/'>summary</a><a href='/guix/refs/?id=efe027b1e02cfa03fa65743e42393898230194be'>refs</a><a class='active' href='/guix/log/nix/nix-daemon'>log</a><a href='/guix/tree/nix/nix-daemon?id=efe027b1e02cfa03fa65743e42393898230194be'>tree</a><a href='/guix/commit/nix/nix-daemon?id=efe027b1e02cfa03fa65743e42393898230194be'>commit</a><a href='/guix/diff/nix/nix-daemon?id=efe027b1e02cfa03fa65743e42393898230194be'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/nix/nix-daemon'>
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<tr><td><span title='2023-12-11 23:18:53 +0100'>2023-12-11</span></td><td><a href='/guix/commit/nix/nix-daemon?id=1e47148f46e31eb99ce8ec7bc12232cf50d0ebec'>daemon: Implement ‘substitute-urls’ RPC.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/libstore/worker-protocol.hh (PROTOCOL_VERSION): Bump.
(WorkerOp): Add ‘wopSubstituteURLs’.
* nix/nix-daemon/nix-daemon.cc (performOp): Implement it.
* guix/store.scm (%protocol-version): Bump.
(operation-id): Add ‘substitute-urls’.
(substitute-urls): New procedure.
* tests/store.scm ("substitute-urls, default")
("substitute-urls, client-specified URLs")
("substitute-urls, disabled"): New tests.

Change-Id: I2c0119500c3a1eecfa5ebf32463ffb0f173161de
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-04-14 14:48:20 +0200'>2022-04-14</span></td><td><a href='/guix/commit/nix/nix-daemon?id=5f74169e8e03e64a15499866c6a6de9f38d36f2d'>daemon: Support systemd-style socket activation.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/nix-daemon/guix-daemon.cc (SD_LISTEN_FDS_START): New macro.
(systemd_activation_sockets): New function.
(main): Use it.  Remove obsolete 'printMsg' call.
* doc/guix.texi (Invoking guix-daemon): Document socket activation.
</span></span></td><td>Ludovic Courtès</td></tr>