Upgrade pinned rust version from 1.79 to 1.81

This matches the version shipped w/ NixOS 24.11.

Author: flihp

rust-toolchain.toml

@@ -1,2 +1,2 @@
 [toolchain]
-channel = "1.79"
+channel = "1.81"

src/secret_writer.rs

@@ -163,7 +163,7 @@ impl SecretWriter for PrinterSecretWriter {
             if i % 4 == 0 {
                 print_file.write_all(&[CR, LF])?;
             }
-            print_file.write_all(&[b'\t'])?;
+            print_file.write_all(b"\t")?;
             print_file.write_all(chunk)?;
         }
 
@@ -220,7 +220,7 @@ impl SecretWriter for PrinterSecretWriter {
             if i % 4 == 0 {
                 print_file.write_all(&[CR, LF])?;
             }
-            print_file.write_all(&[b'\t'])?;
+            print_file.write_all(b"\t")?;
             print_file.write_all(chunk)?;
         }