feat: add fetch_head configuration option into brew (#679)

src/steps/os/unix.rs

@@ -285,10 +285,15 @@ pub fn run_brew_formula(ctx: &ExecutionContext, variant: BrewVariant) -> Result<
     let run_type = ctx.run_type();
 
     variant.execute(run_type).arg("update").status_checked()?;
-    variant
-        .execute(run_type)
-        .args(["upgrade", "--formula"])
-        .status_checked()?;
+
+    let mut command = variant.execute(run_type);
+    command.args(["upgrade", "--formula"]);
+
+    if ctx.config().brew_fetch_head() {
+        command.arg("--fetch-HEAD");
+    }
+
+    command.status_checked()?;
 
     if ctx.config().cleanup() {
         variant.execute(run_type).arg("cleanup").status_checked()?;