fix: ensure macOS/Linux compatibility in polish-junit target

[silvi-t]

Description

• Improved the polish-junit Makefile target to ensure cross-platform compatibility between macOS and Linux

Changes

• Makefile: Refactored polish-junit target for macOS/Linux compatibility
  • Replaced zcat command with gunzip -c (works on both macOS and Linux)
  • Added check for junit XML files existence before processing
  • Added file existence validation within the loop
  • Improved error handling with explicit exit code when no files found
  • Removed error suppression (-rm) that was marked as "dangerous" - now only deletes files created in the same command block
  • Eliminated bashisms in favor of POSIX-compliant shell syntax for better cross-platform portability

Verification steps

1. First, generate junit XML files by running tests:

   make testsuite/tests/<test_path> junit=1

2. Verify the polish-junit target processes the files correctly:

   make polish-junit

3. Or run make reportportal to test the full workflow (ensure all required environment variables are set: RP_TOKEN, REPORTPORTAL, RP_LAUNCH_NAME, RP_PROJECT, REQUESTS_CA_BUNDLE)
4. Test on both macOS and Linux environments to ensure cross-platform compatibility

[emmaaroche]

Ran through verification steps and looks good on macOS 👍