releases/15.0R/relnotes: Update contrib versions and commit hashes
According to the output of:
git log --first-parent -E --grep "merge" --grep "[mM][fF][vV]" --grep='[rR][eE][lL]([eE][aA][sS][eE]:space:+)[nN][oO][tT][eE]' origin/releng/14.0..origin/releng/15.0
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