Add gha cache

[psantus]

Use gha cache, fixed version after #628

Root Cause

The original PR changed from docker build to docker buildx build --load, but this exposed an existing bug in the Makefile's image naming. When building layers like layers/sqlsrv, the image was tagged as
bref/layers/sqlsrv-php-82 instead of bref/sqlsrv-php-82, causing the test step to fail with:

ERROR: pull access denied, repository does not exist or may require authorization:
server message: insufficient_scope: authorization failed

Fix Applied

Updated the Makefile to strip the layers/ directory prefix from image names:

1. Line 10: Changed bref/${1}-php-${2} to bref/$(notdir ${1})-php-${2} in the build_docker_image macro
2. Line 41: Changed TARGET_IMAGE=$${dir}-php-$${php_version} to TARGET_IMAGE=$$(basename $${dir})-php-$${php_version}
3. Lines 42-43: Updated test image references to use $$(basename $${dir}) instead of $${dir}

This ensures images are correctly tagged as bref/sqlsrv-php-82 (without the layers/ prefix), matching what the test Dockerfile expects.

Testing

The fix ensures that:

• Build images are properly tagged and available for subsequent test steps
• GHA cache continues to work as intended
• No impact on local development workflow