fix: propagate include vars in multi-level includes (#1256)

testdata/include_with_vars_multi_level/Taskfile.yml

@@ -0,0 +1,17 @@
+version: "3"
+
+includes:
+  lib:
+    taskfile: lib/Taskfile.yml
+    internal: true
+  foo:
+    taskfile: foo/Taskfile.yml
+  bar:
+    taskfile: bar/Taskfile.yml
+
+tasks:
+  default:
+    cmds:
+      - task: lib:greet
+      - task: foo:lib:greet
+      - task: bar:lib:greet

testdata/include_with_vars_multi_level/bar/Taskfile.yml

@@ -0,0 +1,7 @@
+version: "3"
+
+includes:
+  lib:
+    taskfile: ../lib/Taskfile.yml
+    vars:
+      RECEIVER: "bar"

testdata/include_with_vars_multi_level/foo/Taskfile.yml

@@ -0,0 +1,7 @@
+version: "3"
+
+includes:
+  lib:
+    taskfile: ../lib/Taskfile.yml
+    vars:
+      RECEIVER: "foo"

testdata/include_with_vars_multi_level/lib/Taskfile.yml

@@ -0,0 +1,9 @@
+version: "3"
+
+vars:
+  RECEIVER: "world"
+
+tasks:
+  greet:
+    cmds:
+      - echo 'Hello {{.RECEIVER}}'