t/lib-httpd: pass GIT_TEST_SIDEBAND_ALL through Apache

07c3c2aa ("tests: define GIT_TEST_SIDEBAND_ALL", 2019-01-16) added
GIT_TEST_SIDEBAND_ALL to the apache.conf PassEnv list.  Avoid warnings
from Apache when the variable is unset, as we do for GIT_VALGRIND* and
GIT_TRACE, from f6288254 ("t/lib-httpd: handle running under
--valgrind", 2012-07-24) and 89c57ab3 ("t: pass GIT_TRACE through
Apache", 2015-03-13), respectively.

Signed-off-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-httpd.sh

@@ -91,6 +91,7 @@ HTTPD_DOCUMENT_ROOT_PATH=$HTTPD_ROOT_PATH/www
 # hack to suppress apache PassEnv warnings
 GIT_VALGRIND=$GIT_VALGRIND; export GIT_VALGRIND
 GIT_VALGRIND_OPTIONS=$GIT_VALGRIND_OPTIONS; export GIT_VALGRIND_OPTIONS
+GIT_TEST_SIDEBAND_ALL=$GIT_TEST_SIDEBAND_ALL; export GIT_TEST_SIDEBAND_ALL
 GIT_TRACE=$GIT_TRACE; export GIT_TRACE
 if ! test -x "$LIB_HTTPD_PATH"