CI/Cirrus: Separate make install into own step

This way we keep the output shown in the compile section shorter and more readable.
Remove also the filtering by grep since FreeBSD does not use bash as default shell breaking PIPESTATUS.

.cirrus.yml

@@ -14,7 +14,10 @@ task:
 
   build_script:
     - cd build
-    - make -j3 | grep --line-buffered -Ev '^(cp lib\/|Installing.+\.pm|-- Installing:)' && (exit ${PIPESTATUS[0]})
+    - make -j3
+
+  install_script:
+    - cd build
     - make install
 
   test_script: