'use 5.41' affects current line source::encoding

Previously it didn't take effect until subsequent lines

Fixes #23881

Author: ysth

lib/source/source_encoding.t

@@ -44,8 +44,13 @@ if (fresh_perl_like(<<~'EOT',
                     EOT
                 "",
                 { }, "source encoding can be turned off");
+    fresh_perl_like(<<~'EOT',
+                 use v5.41.0; my $var = "¶";
+                 EOT
+                qr/Use of non-ASCII character 0x[[:xdigit:]]{2} illegal/,
+                { }, ">= 'use statement affects rest of current line'");
 }
-else { # Above test depends on the previous one; if that failed, use this
+else { # Above tests depend on the previous one; if that failed, use this
        # alternate one
     fresh_perl_is(<<~'EOT',
                     use source::encoding 'ascii';

op.c

@@ -8487,6 +8487,7 @@ Perl_utilize(pTHX_ int aver, I32 floor, OP *version, OP *idop, OP *arg)
         else {
             PL_hints &= ~HINT_ASCII_ENCODING;
         }
+        notify_parser_that_encoding_changed();
 
         PL_prevailing_version = shortver;
     }

pod/perldelta.pod

@@ -381,7 +381,8 @@ manager will later use a regex to expand these into links.
 
 =item *
 
-XXX
+S<C<use 5.42>> now turns on S<C<use source::encoding "ascii">> for the
+remainder of the line (besides subsequent lines). [GH #23881]
 
 =back