Force use of BoostConfig.cmake as requested by CMake 3.30

Without this change CMake 3.30 prints a warning, see CMP0167.

See !4706 (merged) too.

added all-slots label

assigned to @clemenci

• [2024-10-17 00:11] Validation started with lhcb-run2-gaudi-head#852
• [2024-10-17 00:11] Validation started with lhcb-run2-patches#1581
• [2024-10-17 11:28] Validation started with lhcb-run2-gaudi-head#853
• [2024-10-17 15:01] Validation started with lhcb-run2-gaudi-head#854
• [2024-10-18 00:15] Validation started with lhcb-run2-gaudi-head#855
• [2024-10-18 00:15] Validation started with lhcb-run2-patches#1582

added Configuration legacy modernisation labels and removed all-slots label

mentioned in commit 140506d6

merged