ci: add more ARM build configurations to CI and release workflows

... it turns out that rustembedded/cross:armv7-unknown-linux-musleabi
doesn't exist. And looking more closely, it looks like the Cross project
has decided to shake things up and publish images to ghcr instead. So we
migrate everything over to that.

tests/misc.rs

@@ -411,7 +411,7 @@ rgtest!(include_zero, |dir: Dir, mut cmd: TestCommand| {
     cmd.args(&["--count", "--include-zero", "nada"]);
     cmd.assert_err();
 
-    let output = cmd.cmd().output().unwrap();
+    let output = cmd.raw_output();
     let stdout = String::from_utf8_lossy(&output.stdout);
     let expected = "sherlock:0\n";
 
@@ -423,7 +423,7 @@ rgtest!(include_zero_override, |dir: Dir, mut cmd: TestCommand| {
     cmd.args(&["--count", "--include-zero", "--no-include-zero", "nada"]);
     cmd.assert_err();
 
-    let output = cmd.cmd().output().unwrap();
+    let output = cmd.raw_output();
     let stdout = String::from_utf8_lossy(&output.stdout);
     assert!(stdout.is_empty());
 });