uri: mark the parser source file as generated

The motivation is to exclude the file from diffs on GitHub's web
interface [1] and to exclude it from checkpatch checks [2].

[1]: https://docs.github.com/en/repositories/working-with-files/managing-files/customizing-how-changed-files-appear-on-github
[2]: https://github.com/tarantool/checkpatch/pull/75

NO_DOC=the patch is about the development process, it doesn't change
       anything in the shipped product
NO_CHANGELOG=see NO_DOC
NO_TEST=see NO_DOC

(cherry picked from commit fbea9862b087e161a48dc0ac181a1da06cc0ce9d)

.gitattributes

@@ -8,3 +8,4 @@
 *.hpp diff=cpp
 *.c++ diff=cpp
 *.h++ diff=cpp
+src/lib/uri/uri_parser.c linguist-generated=true