merge revision(s) 7a05dbc: [Backport #21561]

	File.dirname: return consistent encoding for `"."`

	[Bug #21561]

	It's preferable if the method is consistent in the encoding in
	the returned string.

Author: k0kubun

file.c

@@ -4947,8 +4947,11 @@ rb_file_dirname_n(VALUE fname, int n)
             break;
         }
     }
-    if (p == name)
-        return rb_usascii_str_new2(".");
+    if (p == name) {
+        dirname = rb_str_new(".", 1);
+        rb_enc_copy(dirname, fname);
+        return dirname;
+    }
 #ifdef DOSISH_DRIVE_LETTER
     if (has_drive_letter(name) && isdirsep(*(name + 2))) {
         const char *top = skiproot(name + 2, end, enc);

version.h

@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 5
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 53
+#define RUBY_PATCHLEVEL 54
 
 #include "ruby/version.h"
 #include "ruby/internal/abi.h"