Allow BUILDKITE_TAG to be empty (#365)

* Allow `BUILDKITE_TAG` to be empty

* sign treehashes

Author: staticfloat

pipelines/main/launch_signed_jobs.yml.signature

@@ -1,2 +1 @@
-Salted__V:l*SY'��rc�\b���9�T�nX ��vUd"�w�~0B����0�������&����7�^
-|IKg�v<;T�M��H���	
+Salted__�@E0���P)��z2I��c�E����L���dY��Hn��A��\Y����"AtKsUL��3-�f����H�7�OA̒�Œ.�ʾ��O

pipelines/main/launch_upload_jobs.yml.signature

@@ -1 +1 @@
-Salted__W�9�Q��h�(\k�,����E�����������@�F.ؖAj#�A�$�[�+j
�;[����|�mD��{���}��U�
+Salted__���|H��$҂ޖ�-��]x����#��yB�.j�I�9�Gs�X�j̹{L�Nȁi�\~F�WW���f�V"s?�>�X � j�

pipelines/scheduled/coverage/coverage.yml.signature

@@ -1 +1 @@
-Salted__g�� ���T{£3liշ�D(X��sp�a�K�p��G�g����`!�F�M�$cp����D�J�{��%�bo�d�02�ѳ=G��H�J��
+Salted__Z5uI/c����u����d�*�)y��l���B[/�R�w�M�m��e_p׵z%^D��4o��
�
�=U-��'��t�P�4�B�

pipelines/scheduled/launch_signed_jobs.yml.signature

@@ -140,7 +140,7 @@ S3_BUCKET_PREFIX="${S3_BUCKET_PREFIX:-bin}"
 # We generally upload to multiple upload targets
 UPLOAD_TARGETS=()
 
-if [[ "${BUILDKITE_BRANCH}" == master ]] || [[ "${BUILDKITE_BRANCH}" == release-* ]] || [[ "${BUILDKITE_TAG}" == v* ]]; then
+if [[ "${BUILDKITE_BRANCH}" == master ]] || [[ "${BUILDKITE_BRANCH}" == release-* ]] || [[ "${BUILDKITE_TAG:-}" == v* ]]; then
     # First, we have the canonical fully-specified upload target
     UPLOAD_TARGETS+=( "${S3_BUCKET}/${S3_BUCKET_PREFIX}/${OS?}/${ARCH?}/${MAJMIN?}/julia-${TAR_VERSION?}-${OS?}-${ARCH?}" )