Set TERM to prevent No entry for terminal type "unknown" messages during fetch

Summary:
Fetches cause output in `/var/tmp/phd/log/daemons.log` as
follows:
```
PHLOG: 'Unexpected output while updating repository "rREPONAME": No entry for terminal type "unknown";
using dumb terminal settings.
' at [/path/to/phabricator/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php:455]
```

These warnings come from PHP itself.  Silence these warnings by providing a
known value for `TERM` before shelling out to the PHP script.

See also D9744 (reverted in D11644) and T4990/T7119, which are a similar issue,
but in the pre-receive hooks, not the pull daemons.

Test Plan:
Enabled in production, observed errors to be silenced and
no SSH hangs

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D17100

src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php

@@ -272,6 +272,11 @@ final class PhabricatorRepositoryPullLocalDaemon
 
     $future->setTimeout($timeout);
 
+    // The default TERM inherited by this process is "unknown", which causes PHP
+    // to produce a warning upon startup.  Override it to squash this output to
+    // STDERR.
+    $future->updateEnv('TERM', 'dumb');
+
     return $future;
   }