add method to rust-analyzer macro server

Author: beepster4096

src/tools/rust-analyzer/crates/proc-macro-srv/src/abis/abi_sysroot/ra_server.rs

@@ -72,6 +72,10 @@ impl server::Types for RustAnalyzer {
 }
 
 impl server::FreeFunctions for RustAnalyzer {
+    fn injected_env_var(&mut self, _var: &str) -> Option<String> {
+        None
+    }
+
     fn track_env_var(&mut self, _var: &str, _value: Option<&str>) {
         // FIXME: track env var accesses
         // https://github.com/rust-lang/rust/pull/71858