Docs for source_buildenv (#3493)

* Docs for source_buildenv

* Update reference/conanfile/attributes/sources.inc

Co-authored-by: James <memsharded@gmail.com>

* Update reference/conanfile/attributes/sources.inc

Co-authored-by: James <memsharded@gmail.com>

* Update reference/conanfile/attributes/sources.inc

* Update reference/conanfile/attributes/sources.inc

Co-authored-by: Carlos Zoido <mrgalleta@gmail.com>

* Update reference/conanfile/attributes/sources.inc

* Update reference/conanfile/attributes/sources.inc

---------

Co-authored-by: James <memsharded@gmail.com>
Co-authored-by: Carlos Zoido <mrgalleta@gmail.com>

reference/conanfile/attributes/sources.inc

@@ -111,4 +111,25 @@ For example, a *conandata.yml* with information about sources that looks like th
 .. code-block:: python
 
     def source(self):
-        tools.get(**self.conan_data["sources"][self.version])
+        get(self, **self.conan_data["sources"][self.version])
+
+source_buildenv
+---------------
+
+Boolean attribute to opt-out from injecting the :ref:`VirtualBuildEnv<conan_tools_env_virtualbuildenv>` generated environment while running the `source()` method.
+
+Setting this attribute to `False` (default value `True`) will prevent Conan from injecting the ``VirtualBuildEnv`` generated environment from tool requires
+when executing the `source()` method.
+
+.. code-block:: python
+   :emphasize-lines: 4,5,8
+
+    class MyConan:
+       name = "mylib"
+       version = "1.0.0"
+       source_buildenv = False
+       tool_requires = "7zip/1.2.0"
+
+       def source(self):
+           get(self, **self.conan_data["sources"][self.version])
+           self.run("7z x *.zip -o*")  ## Error! tool require not available