selftests: add kselftest_install to .gitignore

Add kselftest_install directory to the .gitignore which is created while
creation of tar ball of objects:
make -C tools/testing/selftests gen_tar
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/.gitignore

@@ -3,6 +3,7 @@ gpiogpio-event-mon
 gpiogpio-hammer
 gpioinclude/
 gpiolsgpio
+kselftest_install/
 tpm2/SpaceTest.log
 
 # Python bytecode and cache