fix: uses sh, not bash

Author: beckermr

.readthedocs.yaml

@@ -10,7 +10,7 @@ build:
   commands:
     - git fetch --unshallow || true
     - git fetch --all --tags || true
-    - if [[ ${READTHEDOCS_VERSION_TYPE} == "tag" ]]; then git checkout ${READTHEDOCS_GIT_IDENTIFIER}; fi
+    - if [ "${READTHEDOCS_VERSION_TYPE}" = "tag" ]; then git checkout ${READTHEDOCS_GIT_IDENTIFIER}; fi
     - pip install uv
     - uv sync --extra docs
     - uv run sphinx-build -b html docs $READTHEDOCS_OUTPUT/html