Add #[must_use] to is_condition tests

A continuation of #89718.

library/std/src/fs.rs

@@ -1005,6 +1005,7 @@ impl Metadata {
     ///     Ok(())
     /// }
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_dir(&self) -> bool {
         self.file_type().is_dir()
@@ -1033,6 +1034,7 @@ impl Metadata {
     ///     Ok(())
     /// }
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_file(&self) -> bool {
         self.file_type().is_file()
@@ -1059,6 +1061,7 @@ impl Metadata {
     ///     Ok(())
     /// }
     /// ```
+    #[must_use]
     #[unstable(feature = "is_symlink", issue = "85748")]
     pub fn is_symlink(&self) -> bool {
         self.file_type().is_symlink()
@@ -1306,6 +1309,7 @@ impl FileType {
     ///     Ok(())
     /// }
     /// ```
+    #[must_use]
     #[stable(feature = "file_type", since = "1.1.0")]
     pub fn is_dir(&self) -> bool {
         self.0.is_dir()
@@ -1338,6 +1342,7 @@ impl FileType {
     ///     Ok(())
     /// }
     /// ```
+    #[must_use]
     #[stable(feature = "file_type", since = "1.1.0")]
     pub fn is_file(&self) -> bool {
         self.0.is_file()
@@ -1373,6 +1378,7 @@ impl FileType {
     ///     Ok(())
     /// }
     /// ```
+    #[must_use]
     #[stable(feature = "file_type", since = "1.1.0")]
     pub fn is_symlink(&self) -> bool {
         self.0.is_symlink()