git-p4: missing she-bang line in t9804 confuses prove

Without the magic line, prove shows lots and lots of errors:
% prove ./t9804-git-p4-label.sh
./t9804-git-p4-label.sh .. syntax error at ./t9804-git-p4-label.sh line 3, near ". ."
...

When #!/bin/sh is added, tests are skipped (I have no p4d).

Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9804-git-p4-label.sh

@@ -1,3 +1,5 @@
+#!/bin/sh
+
 test_description='git-p4 p4 label tests'
 
 . ./lib-git-p4.sh