Use regex to properly select Go test runnable (#13750)

This is already done when selecting a subtest; by wrapping the test name
with `^{}$` the runnable will avoid selecting additional tests with the
same prefix.

Without this fix, selecting the runnable for `TestExample` will also run
`TestExample2`.

Release Notes:

- Fixed Golang tasks spawning tests starting with the current function name and not using the exact match.

crates/languages/src/go.rs

@@ -518,7 +518,7 @@ impl ContextProvider for GoContextProvider {
                     "test".into(),
                     GO_PACKAGE_TASK_VARIABLE.template_value(),
                     "-run".into(),
-                    VariableName::Symbol.template_value(),
+                    format!("^{}$", VariableName::Symbol.template_value(),),
                 ],
                 tags: vec!["go-test".to_owned()],
                 ..TaskTemplate::default()