package/ci: reduce parallelism even further.

Damnit, I wonder where is it using so much memory and why.

package/ci/circleci.yml

@@ -273,11 +273,11 @@ jobs:
     steps:
     - install-base-linux:
         extra: libgl1-mesa-dev libsdl2-dev libglfw3-dev libopenal-dev libvulkan-dev
-    # In this case it gets stuck even with 24 jobs. Only on GCC, usually when
+    # In this case it gets stuck even with 20 jobs. Only on GCC, usually when
     # the huge TradeAbstractImporterTest / TradeMaterialDataTest get involved.
     # TODO: revisit when we get rid of more STL / deprecated includes
     - cap-ninja-jobs:
-        count: 20
+        count: 16
     - install-gcc-4_8
     - install-cmake:
         version: "3.4.3"
@@ -311,11 +311,11 @@ jobs:
     steps:
     - install-base-linux:
         extra: cmake libsdl2-dev libglfw3-dev libvulkan-dev wget unzip
-    # It crashes with the default setting. Only on GCC, usually when the huge
+    # In this case it gets stuck even with 24 jobs. Only on GCC, usually when
-    # TradeAbstractImporterTest / TradeMaterialDataTest / TradeSceneDataTest
+    # the huge TradeAbstractImporterTest / TradeMaterialDataTest get involved.
-    # get involved.
     # TODO: revisit when we get rid of more STL / deprecated includes
-    - cap-ninja-jobs
+    - cap-ninja-jobs:
+        count: 20
     - install-gcc-4_8
     - install-swiftshader-vulkan:
         build: ubuntu-18.04
@@ -418,13 +418,12 @@ jobs:
     steps:
     - install-base-linux:
         extra: libgl1-mesa-dev libsdl2-dev libglfw3-dev libopenal-dev libvulkan-dev
-    # It crashes with the default setting. Only on GCC, usually when the huge
+    # In this case it gets stuck even with 20 jobs, usually when the huge
     # TradeAbstractImporterTest / TradeMaterialDataTest / TradeSceneDataTest
-    # get involved. 24 is not enough, as everything goes significantly faster
+    # get involved.
-    # and so the heavy jobs are likely to get scheduled together.
     # TODO: revisit when we get rid of more STL
     - cap-ninja-jobs:
-        count: 20
+        count: 16
     - install-gcc-4_8
     - install-cmake:
         version: "3.4.3"