.gitignore: Ignore more files

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/657>

.gitignore

@@ -1,9 +1,20 @@
 _build/
+debian/.debhelper/
+debian/cargo/registry/
+debian/cargo/.*cache*
+debian/debhelper-build-stamp
+debian/files
+debian/*.substvars
+debian/squeekboard/
+debian/squeekboard-devel/
+debian/tmp/
+meson_Cargo.toml.in
 po/squeekboard.pot
 po/*.mo
 TAGS
 tags
 target/
+vendor/
 vgdump
 *.swp
 *~