Merge pull request #15742 from branchvincent/std_pip_args

formula: fix `std_pip_args` with empty prefix

Library/Homebrew/formula.rb

@@ -1630,7 +1630,7 @@ class Formula
   def std_pip_args(prefix: self.prefix, build_isolation: false)
     args = ["--verbose", "--no-deps", "--no-binary=:all:", "--ignore-installed",
             "--use-feature=no-binary-enable-wheel-cache"]
-    args << "--prefix=#{prefix}" if prefix.present?
+    args << "--prefix=#{prefix}" if prefix
     args << "--no-build-isolation" unless build_isolation
     args
   end