chore: gitignore vkd3d-proton/DXVK runtime shader caches

The Wine canary build drops vkd3d-proton.cache into the working dir.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -11,3 +11,8 @@ audit-*.md
 *.stdout
 *.stderr
 *.log
+
+# Runtime cache artifacts (vkd3d-proton / DXVK shader caches dropped into the
+# working dir by the Wine canary build)
+vkd3d-proton.cache*
+*.dxvk-cache