fix: update gitmodules-shas to current submodule SHAs

The gitmodules-shas file was pointing to an old libKriging commit
(169337800d) that still had exportClasses(NuggetKM, NoiseKM) in its
NAMESPACE. When devtools::install_github downloads the GitHub archive
(no .git directory), setup.sh reads this file to clone the submodule
at the pinned SHA — causing the old NAMESPACE (with NuggetKM/NoiseKM
as S4 classes) to be used, triggering load failure.

Updated to current submodule HEAD (87651a24) which has the clean
NAMESPACE without these class exports.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: yannrichet

tools/gitmodules-shas

@@ -1,5 +1,5 @@
 # This file records the specific commit SHAs for each submodule
 # It is automatically generated and should be updated when submodules are updated
 # Format: <submodule_path> <commit_sha>
-src/libK 169337800d6dcbaa64c203186d3bdc34d291bafa
+src/libK 87651a2436dda9439888c9acb1ef363d35ec607d
 src/slapack 72a7f3753e02b0471e93296f2b22877c6fee7328