coverage: Rename the run-coverage test mode to coverage-run

This makes it more consistent with the `coverage-map` mode and the shared
`tests/coverage` test directory.

tests/coverage-run-rustdoc/auxiliary/doctest_crate.rs

@@ -0,0 +1,9 @@
+/// A function run only from within doctests
+pub fn fn_run_in_doctests(conditional: usize) {
+    match conditional {
+        1 => assert_eq!(1, 1), // this is run,
+        2 => assert_eq!(1, 1), // this,
+        3 => assert_eq!(1, 1), // and this too
+        _ => assert_eq!(1, 2), // however this is not
+    }
+}