Projects: Revert "Merge branch 'lcg101atlas28_20221014' into 'master'"

This reverts merge request !57540 (merged)

Revert back to LCG_101_ATLAS_26 since the LCG_externals_x86_64-centos7-gcc11-opt.txt is broken in the LCG RPMs as discussed in https://its.cern.ch/jira/browse/ATLINFR-4722 and reported in https://sft.its.cern.ch/jira/projects/SPI/issues/SPI-2225

Tagging @nstyles, @akraszna, @tsulaia for info

No full-build/full-unit-tests this time - @tsulaia please merge this MR in case there is no reasonable progress on the SPI jira ticket.