CavernBkgGenerator: Fix C++/fortran declaration inconsistency.

Fix inconsistencies in function declarations between C++/fortran. Fixes warnings seen in an LTO build.

This merge request affects 1 package:

• Generators/CavernBkgGenerator

This merge request affects 2 files:

• Generators/CavernBkgGenerator/CavernBkgGenerator/BkgOut.h
• Generators/CavernBkgGenerator/src/GenerateCavernBkg.cxx

added Generators main review-pending-level-1 labels

CI Result SUCCESS (hash 5eb3621e)

	Athena
externals
cmake
make
tests

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Athena: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-EL9 8462] (remote access info)

removed review-pending-level-1 label

added review-approved label

merged

mentioned in commit 5ee6ec28