Fix local builds of feedstock submodules

[jakirkham]

Fixes #1825

In conda-smithy version 3.28.0 logic was added to store metadata about CI ( #1577 ) like the sha of the feedstock that was used to build. As the sha variable may not be set when running locally, logic was added with the container to determine this by running git rev-parse to fill in this value

conda-smithy/conda_smithy/templates/build_steps.sh.tmpl

Lines 86 to 90 in 00fcb77

	if [[ "${sha:-}" == "" ]]; then
	pushd ${FEEDSTOCK_ROOT}
	sha=$(git rev-parse HEAD)
	popd
	fi

While this works in the simple case of cloning a feedstock directly, it does not work in the case of building a feedstock from a submodule as is the case with the feedstocks repo. This is due to the fact that the .git repo information is not full available within the Docker container as it does not exist in the feedstock that is mounted (and is not otherwise provided for).

However this information is available before spinning up the Docker container. So this PR moves the logic to fill in sha to precede spinning up the Docker container. This is equivalent to the behavior already present in the local macOS builds, which don't use containers

conda-smithy/conda_smithy/templates/run_osx_build.sh.tmpl

Lines 68 to 70 in 00fcb77

	if [[ "${sha:-}" == "" ]]; then
	sha=$(git rev-parse HEAD)
	fi

Closes conda-forge/ca-certificates-feedstock#64 (used for testing these changes)

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[jakirkham]

Tested these changes with the ca-certificates feedstock by building on CI and locally (using the feedstocks submodule for ca-certificates). Both seem to work ok

xref: conda-forge/ca-certificates-feedstock#64

[isuruf]

Thanks