Drop check for mingw32-make.

From what I can tell, it is no longer necessary on GitHub Actions.
This removes it to help simplify things.

tests/testsuite/jobserver.rs

@@ -58,17 +58,8 @@ fn jobserver_exists() {
     p.cargo("build -j2").run();
 }
 
-#[cargo_test]
+#[cargo_test(requires_make)]
 fn makes_jobserver_used() {
-    let make = if cfg!(windows) {
-        "mingw32-make"
-    } else {
-        "make"
-    };
-    if !is_ci() && Command::new(make).arg("--version").output().is_err() {
-        return;
-    }
-
     let p = project()
         .file(
             "Cargo.toml",
@@ -162,7 +153,7 @@ all:
         drop((a2, a3));
     });
 
-    p.process(make)
+    p.process("make")
         .env("CARGO", cargo_exe())
         .env("ADDR", addr.to_string())
         .arg("-j2")
@@ -172,15 +163,6 @@ all:
 
 #[cargo_test]
 fn jobserver_and_j() {
-    let make = if cfg!(windows) {
-        "mingw32-make"
-    } else {
-        "make"
-    };
-    if !is_ci() && Command::new(make).arg("--version").output().is_err() {
-        return;
-    }
-
     let p = project()
         .file("src/lib.rs", "")
         .file(
@@ -192,7 +174,7 @@ all:
         )
         .build();
 
-    p.process(make)
+    p.process("make")
         .env("CARGO", cargo_exe())
         .arg("-j2")
         .with_stderr(