Fix tests with binutils 2.41

The tests broke on my machine because of
bminor/binutils-gdb@014a602
which was fixed half a year later by
bminor/binutils-gdb@f82ee0c
so the only binutils version affected is 2.41.

Nevertheless, apparently using objcopy output to pipe is not something
officially supported, so we can avoid such issues in the future by using
another temporary file.

test/test_core.py

@@ -263,7 +263,7 @@ def test_asm_source(self):
         self.base_dir = "test/asm/"
         self.bin_src = []
 
-        with tempfile.NamedTemporaryFile() as asm_tmp:
+        with tempfile.NamedTemporaryFile() as asm_tmp, tempfile.NamedTemporaryFile() as bin_tmp:
             subprocess.check_call(
                 [
                     "riscv64-unknown-elf-as",
@@ -276,9 +276,10 @@ def test_asm_source(self):
                     self.base_dir + self.source_file,
                 ]
             )
-            code = subprocess.check_output(
-                ["riscv64-unknown-elf-objcopy", "-O", "binary", "-j", ".text", asm_tmp.name, "/dev/stdout"]
+            subprocess.check_call(
+                ["riscv64-unknown-elf-objcopy", "-O", "binary", "-j", ".text", asm_tmp.name, bin_tmp.name]
             )
+            code = bin_tmp.read()
             for word_idx in range(0, len(code), 4):
                 word = code[word_idx : word_idx + 4]
                 bin_instr = int.from_bytes(word, "little")