Add fake Source function and models

Author: egregius313

go/ql/test/library-tests/semmle/go/dataflow/flowsources/local/database/go.mod

@@ -6,4 +6,5 @@ require (
 	gorm.io/gorm v1.23.0
 	github.com/jmoiron/sqlx v1.4.0
 	go.mongodb.org/mongo-driver/mongo v1.17.2
+	github.com/nonexistent/sources v0.0.0-20250300000000-000000000000
 )

go/ql/test/library-tests/semmle/go/dataflow/flowsources/local/database/source.ext.yml

@@ -3,4 +3,9 @@ extensions:
       pack: codeql/threat-models
       extensible: threatModelConfiguration
     data:
-      - ["database", true, 0]
+      - ["database", true, 0]
+  - addsTo:
+      pack: codeql/go-all
+      extensible: sourceModel
+    data:
+      - ["github.com/nonexistent/sources", "", False, "Source", "", "", "ReturnValue", "database", "manual"]

go/ql/test/library-tests/semmle/go/dataflow/flowsources/local/database/test.ext.yml

@@ -5,3 +5,9 @@ extensions:
       extensible: threatModelConfiguration
     data:
       - ["database", true, 0]
+
+  - addsTo:
+      pack: codeql/go-all
+      extensible: sourceModel
+    data:
+      - ["github.com/nonexistent/sources", "", False, "Source", "", "", "ReturnValue", "database", "manual"]

go/ql/test/library-tests/semmle/go/dataflow/flowsources/local/database/vendor/github.com/nonexistent/sources/stub.go

@@ -7,3 +7,6 @@ github.com/jmoiron/sqlx
 # go.mongodb.org/mongo-driver/mongo v1.17.2
 ## explicit
 go.mongodb.org/mongo-driver/mongo
+# github.com/nonexistent/sources v0.0.0-20250300000000-000000000000
+## explicit
+github.com/nonexistent/sources