Rename foo.py to my_gdb_script.py

This makes it easier for maintainers to see what the Python script is for.

tests/run-make/debugger-visualizer-dep-info/main.rs

@@ -1,4 +1,4 @@
-#![debugger_visualizer(gdb_script_file = "foo.py")]
+#![debugger_visualizer(gdb_script_file = "my_gdb_script.py")]
 
 fn main() {
     const _UNUSED: u32 = {

tests/run-make/debugger-visualizer-dep-info/rmake.rs

@@ -6,6 +6,6 @@
 
 fn main() {
     rustc().emit("dep-info").input("main.rs").run();
-    invalid_utf8_contains("main.d", "foo.py");
+    invalid_utf8_contains("main.d", "my_gdb_script.py");
     invalid_utf8_contains("main.d", "my_visualizers/bar.natvis");
 }