ci: Set ZIG_GLOBAL_CACHE_DIR and ZIG_LOCAL_CACHE_DIR earlier.

Otherwise the disk just keeps getting filled up.

Also remove some pointless cleanup commands since the actions/checkout workflow
step already cleans the repository by default.

ci/aarch64-macos-debug.sh

@@ -26,16 +26,15 @@ cd $ZIGDIR
 git fetch --unshallow || true
 git fetch --tags
 
-rm -rf build-debug
-mkdir build-debug
-cd build-debug
-
 # Override the cache directories because they won't actually help other CI runs
 # which will be testing alternate versions of zig, and ultimately would just
 # fill up space on the hard drive for no reason.
 export ZIG_GLOBAL_CACHE_DIR="$PWD/zig-global-cache"
 export ZIG_LOCAL_CACHE_DIR="$PWD/zig-local-cache"
 
+mkdir build-debug
+cd build-debug
+
 PATH="$HOME/local/bin:$PATH" cmake .. \
   -DCMAKE_INSTALL_PREFIX="stage3-debug" \
   -DCMAKE_PREFIX_PATH="$PREFIX" \