[CI/Build] remove .github from .dockerignore, add dirty repo check (#9375)

tools/check_repo.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+# Checks whether the repo is clean and whether tags are available (necessary to correctly produce vllm version at build time)
+
+if ! git diff --quiet; then
+	echo "Repo is dirty" >&2
+
+	exit 1
+fi
+
+if ! git describe --tags; then
+	echo "No tags are present. Is this a shallow clone? git fetch --unshallow --tags" >&2
+
+	exit 1
+fi