Run some disk usage diagnostics at the start of the build

[chrisfenner]

Builds are currently failing with errors like the following from https://github.com/TrustedComputingGroup/pandoc/actions/runs/20356097258:

#37 4093.1    Compiling two-face v0.4.5
#37 4174.6 error: failed to build archive at `/tmp/cargo-installMzHv9Q/release/deps/libaz-06a19f8d2b7d0542.rlib`: No space left on device (os error 28)
#37 4174.6 
#37 4174.6 error: could not compile `az` (lib) due to 1 previous error
#37 4174.7 warning: build failed, waiting for other jobs to finish...
#37 4201.3 error: failed to build archive at `/tmp/cargo-installMzHv9Q/release/deps/libtwo_face-e3b123c8f4afbd07.rlib`: No space left on device (os error 28)
#37 4201.3 
#37 4201.3 error: could not compile `two-face` (lib) due to 1 previous error

Related to #284