Limit all builds to 4 parallel jobs (i.e. make -j4)

.gitlab-ci.yml

@@ -9,6 +9,7 @@ variables:
   #ICINGA_BUILD_TYPE: release
   #ICINGA_BUILD_RELEASE_TYPE:
   #ICINGA_BUILD_UPSTREAM_BRANCH:
+  RPM_BUILD_NCPUS: 4
 
 .build: &build
   stage: build
@@ -92,7 +93,6 @@ build/fedora/34:
   <<: *build
   variables:
     DOCKER_IMAGE: fedora/34
-    RPM_BUILD_NCPUS: '1'
 
 test/fedora/34:
   <<: *test
@@ -110,7 +110,6 @@ build/fedora/33:
   <<: *build
   variables:
     DOCKER_IMAGE: fedora/33
-    RPM_BUILD_NCPUS: '1'
 
 test/fedora/33:
   <<: *test