chore: lower concurrency slightly more (#36335)

Our compilation process is even more memory hungry than we thought. We are still eating up 100% of memory during the heavy build tasks.

Increase the guess at memory per job even more, so that we limit concurrency slightly more. We will keep doing this until our memory consumption dips to ~95%.

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: rix0rrr

build.sh

@@ -100,8 +100,8 @@ fi
 if [[ "$concurrency" == "" ]]; then
     # Auto-limit top-level concurrency to:
     # - available CPUs - 1 to limit CPU load
-    # - total memory / 6GB  (N.B: constant here may need to be tweaked, configurable with $CDKBUILD_MEM_PER_PROCESS)
-    mem_per_process=${CDKBUILD_MEM_PER_PROCESS:-6_000_000_000}
+    # - total memory / 8GB  (N.B: constant here may need to be tweaked, configurable with $CDKBUILD_MEM_PER_PROCESS)
+    mem_per_process=${CDKBUILD_MEM_PER_PROCESS:-8_000_000_000}
     concurrency=$(node -p "Math.max(1, Math.min(require('os').cpus().length - 1, Math.round(require('os').totalmem() / $mem_per_process)))")
     echo "Concurrency: $concurrency"
 fi