Fix make pdk on existing pdk tree
Fix make pdk on existing pdk tree

If make pdk is run on an existing pdk tree, we get an error:

cd /home/anton/pdk.rc6/skywater-pdk && \
	git checkout master && git pull && \
	git checkout -qf 3d7617a1acb92ea883539bcf22a632d6361a5de4
Already on 'master'
Your branch is up to date with 'origin/master'.
Fetching submodule libraries/sky130_fd_io/latest
Could not access submodule 'third_party/make-env'
Fetching submodule libraries/sky130_fd_sc_hvl/latest
Errors during submodule fetch:
	libraries/sky130_fd_io/latest
make: *** [Makefile:76: skywater-pdk] Error 1

This is because we are manually checking out a subset of the submodules.
Add --no-recurse-submodules to git pull to fix this.

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