Makefile: limit scope of format/format-check

We don't want `.git` or `target/` or other misc dirs to be subject to
these phony targets.

Author: cpu

Makefile

@@ -62,14 +62,14 @@ clean:
 	rm -rf target
 
 format:
-	find . \
+	find src tests \
 		-name '*.[c|h]' \
 		! -path "./target/*" \
 		! -wholename './src/rustls.h' | \
 			xargs clang-format -i
 
 format-check:
-	find . \
+	find src tests \
 		-name '*.[c|h]' \
 		! -path "./target/*" \
 		! -wholename './src/rustls.h' | \