debian/rules: work around more flaky git-svn tests

debian/rules: work around more flaky git-svn tests

t9128.4 failed on armel[1]:

 r4 = a73e45a656679dc6e0dde155a11d0c97f5118539 (refs/remotes/mirror/d)
 *** Error in `/usr/bin/perl': free(): invalid pointer: 0x81806da8 ***
 error: git-svn died of signal 6
 not ok 4 - branch uses correct svn-remote

t9167.3 failed in experimental on i386[2] and s390x[3]:

 r6 = c25ca1c3f3fb3b3029ece07c4fad9096818f767c (refs/remotes/origin/tags/tag1)
 error: git-svn died of signal 11
 not ok 3 - git svn branch tests

Omit these tests from the main "make test" run and run them
separately, as was already done for t9128.3.  This should buy some
time to investigate.

[1] https://buildd.debian.org/status/fetch.php?pkg=git&arch=armel&ver=1%3A2.13.2-2&stamp=1498715136&raw=0
[2] https://buildd.debian.org/status/fetch.php?pkg=git&arch=i386&ver=1%3A2.13.2%2Bnext.20170626-1&stamp=1498518903&raw=0
[3] https://buildd.debian.org/status/fetch.php?pkg=git&arch=s390x&ver=1%3A2.13.2%2Bnext.20170626-1&stamp=1498519291&raw=0

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>