Avoid "should be a hash" error

> jobs:sast:variables config should be a hash of key value pairs

plus one more error message for each other job in
lib/gitlab/ci/templates/Security/SAST.gitlab-ci.yml

doc/user/application_security/dast/index.md

@@ -838,7 +838,7 @@ include:
   template: DAST.gitlab-ci.yml
 
 variables:
-  DAST_INCLUDE_ALPHA_VULNERABILITIES: true
+  DAST_INCLUDE_ALPHA_VULNERABILITIES: "true"
 ```
 
 ## Interacting with the vulnerabilities

doc/user/application_security/sast/index.md

@@ -267,7 +267,7 @@ spotbugs-sast:
     - build
   variables:
     MAVEN_REPO_PATH: ./.m2/repository
-    COMPILE: false
+    COMPILE: "false"
   artifacts:
     reports:
       sast: gl-sast-report.json