setup-build-env: support pahole=none input

Allow action caller to skip building pahole by passing 'none' as the
target revision.

See: https://lore.kernel.org/dwarves/8f5711430e4f9bb02fd06d3a5b00d46d8643fea1@linux.dev/
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>

Author: theihor

setup-build-env/build_pahole.sh

@@ -5,6 +5,11 @@ set -eu
 PAHOLE_BRANCH=${PAHOLE_BRANCH:-master}
 PAHOLE_ORIGIN=${PAHOLE_ORIGIN:-https://git.kernel.org/pub/scm/devel/pahole/pahole.git}
 
+if [ "$PAHOLE_BRANCH" == "none" ]; then
+   echo "WARNING: will not build and install pahole, because 'pahole: none' was passed to the action call"
+   exit 0
+fi
+
 source $(cd $(dirname $0) && pwd)/../helpers.sh
 
 foldable start build_pahole "Building pahole"