Set multiple make jobs on CodeQL github workflows

github supports 2 processors right now, although we use nproc instead of
hard coding -j2, so if that ever increases, we will take advantage of it
right away.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Damian Szuberski <szuberskidamian@gmail.com>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #14217

.github/workflows/codeql.yml

@@ -19,6 +19,10 @@ jobs:
         language: [ 'cpp', 'python' ]
 
     steps:
+    - name: Set make jobs
+      run: |
+        echo "MAKEFLAGS=-j$(nproc)" >> $GITHUB_ENV
+
     - name: Checkout repository
       uses: actions/checkout@v3