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
 
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<div class='path'>path: <a href='/guix/log/?id=4ba9f3e0f1484524f91ca1f7ec3a4ce7cb8873ff'>root</a>/<a href='/guix/log/gnu?id=4ba9f3e0f1484524f91ca1f7ec3a4ce7cb8873ff'>gnu</a>/<a href='/guix/log/gnu/services?id=4ba9f3e0f1484524f91ca1f7ec3a4ce7cb8873ff'>services</a>/<a href='/guix/log/gnu/services/auditd.scm?id=4ba9f3e0f1484524f91ca1f7ec3a4ce7cb8873ff'>auditd.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/gnu/services/auditd.scm?id=4ba9f3e0f1484524f91ca1f7ec3a4ce7cb8873ff&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-11-30 01:08:55 +0100'>2021-11-30</span></td><td><a href='/guix/commit/gnu/services/auditd.scm?id=892f1b7273d57b25940700877a02618fe826cc08'>services: Accept &lt;inferior-package&gt;s in lieu of &lt;package&gt;s.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/authentication.scm (fprintd-configuration)
(nslcd-configuration): Substitute file-like objects for package ones.
* gnu/services/cgit.scm (cgit-configuration, opaque-cgit-configuration):
Likewise.
* gnu/services/cups.scm (package-list?, cups-configuration): Likewise.
* gnu/services/dns.scm (verify-knot-configuration)
(ddclient-configuration): Likewise.
* gnu/services/docker.scm (docker-configuration): Likewise.
* gnu/services/file-sharing.scm (transmission-daemon-configuration): Likewise.
* gnu/services/getmail.scm (getmail-configuration): Likewise.
* gnu/services/mail.scm (dovecot-configuration)
(opaque-dovecot-configuration): Likewise.
* gnu/services/messaging.scm (prosody-configuration)
(opaque-prosody-configuration): Likewise.
* gnu/services/monitoring.scm (zabbix-server-configuration)
(zabbix-agent-configuration): Likewise.
* gnu/services/networking.scm (opendht-configuration): Likewise.
* gnu/services/pm.scm (tlp-configuration): Likewise.
* gnu/services/telephony.scm (jami-configuration): Likewise.
* gnu/services/virtualization.scm (libvirt-configuration)
(qemu-guest-agent-configuration): Likewise.
* gnu/services/vpn.scm (openvpn-client-configuration): Likewise.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>