Use /usr/bin/curl to always use the system curl

Avoids using the version in ShellB3, which isn't what we want (And is
busted as a bonus)

csppfetch/__init__.py

@@ -505,7 +505,7 @@ def download_to_file_no_lock(url, dst, fileobj, timeout=HUGE_TIMEOUT):
         more = f"(using temporary file {fileobj.name})"
     logging.debug(f"Downloading {url} to {dst} {more}")
     args = [
-            "curl",
+            "/usr/bin/curl",
             "--location", # Follow redirects
             "--fail", # Exit non-zero on HTTP errors (4xx or 5xx)
             url