fix: interpret-trailer values for Windows

Running `git interpret-trailers` can be difficult on Windows due to
weird/inconsistent/broken command line parsing. Splitting the "--trailer"
flag from its value is a partial mitigation of these problems.

On Windows, Command.arg() does some magic auto-quoting. A value such as
"--trailer=Signed-off-by=Some Name <[email protected]>" will be quoted such
that *some* git executables will interpret the whole shebang as a file
argument. The Git for Windows executable has different (better, probably)
behavior than, for example, git built for MSYS2/MINGW/CRT64 environment.
For the MSYS2 git, this change may work in some cases (e.g. if the trailer
value is all ASCII?), but not in others (e.g. if there are any non-ASCII
characters?).

So, partial mitigation.

Author: jpgrayson

src/stupid/context.rs

@@ -696,14 +696,13 @@ impl<'repo, 'index> StupidContext<'repo, 'index> {
         message: &[u8],
         trailers: impl IntoIterator<Item = (&'a str, &'a str)>,
     ) -> Result<Vec<u8>> {
-        let output = self
-            .git()
-            .arg("interpret-trailers")
-            .args(
-                trailers
-                    .into_iter()
-                    .map(|(trailer, by)| format!("--trailer={trailer}={by}")),
-            )
+        let mut command = self.git();
+        command.arg("interpret-trailers");
+        for (trailer, by) in trailers {
+            command.arg("--trailer");
+            command.arg(format!("{trailer}={by}"));
+        }
+        let output = command
             .stdout(Stdio::piped())
             .in_and_out(message)?
             .require_success("interpret-trailers")?;