Add test for tuple indexed with float in macro input

Author: dtolnay

src/test/ui/tuple/indexing-in-macro.rs

@@ -0,0 +1,9 @@
+// Broken by https://github.com/rust-lang/rust/pull/70420.
+
+macro_rules! m {
+    (.$l:literal) => {};
+}
+
+m!(.0.0); //~ ERROR no rules expected the token `.`
+
+fn main() {}

src/test/ui/tuple/indexing-in-macro.stderr

@@ -0,0 +1,11 @@
+error: no rules expected the token `.`
+  --> $DIR/indexing-in-macro.rs:7:6
+   |
+LL | macro_rules! m {
+   | -------------- when calling this macro
+...
+LL | m!(.0.0);
+   |      ^ no rules expected this token in macro call
+
+error: aborting due to previous error
+