matrix: set jobs to 6

problem: fedora40 on arm64 is taking more than two hours, also runners
have gotten bigger and our job count has not

solution: increase jobs from 4 to 6, we need to see if this causes
failures due to OOM or similar, and possibly decrease the count for the
testing phase

Author: trws

src/test/generate-matrix.py

@@ -83,7 +83,7 @@ def add_build(
         name=None,
         image="fedora40",
         args=default_args,
-        jobs=4,
+        jobs=6,
         env=None,
         docker_tag=False,
         test_s3=False,
@@ -293,7 +293,6 @@ def __str__(self):
     image="bookworm",
     coverage_flags="ci-basic",
     coverage=True,
-    jobs=4,
     args="--with-flux-security --enable-caliper",
 )
 
@@ -311,7 +310,6 @@ def __str__(self):
     coverage_flags="ci-system",
     image="el8",
     coverage=True,
-    jobs=4,
     command_args="--system",
     args="--with-flux-security --enable-caliper",
 )