ecpg: use our instead of my in parse.pl to fix perlcritic complaint

In db0a272d12 I used open(our $something, ...), which perlcritic doesn't
like. It looks like the warning is due to perlcritic knowing about 'my' but
not 'our' when checking for bareword file handles.

However, it's clearly unnecessary to use "our" here, change it to "my".

Via buildfarm member crake and discussion with Tom Lane.

Discussion: https://postgr.es/m/20220718215042.sl3hivoupdb7lkwv@awork3.anarazel.de

src/interfaces/ecpg/preproc/parse.pl

@@ -27,8 +27,8 @@ GetOptions(
 	'parser=s' => \$parser,) or die "wrong arguments";
 
 # open parser / output file early, to raise errors early
-open(our $parserfh, '<', $parser) or die "could not open parser file $parser";
-open(our $outfh, '>', $outfile) or die "could not open output file $outfile";
+open(my $parserfh, '<', $parser) or die "could not open parser file $parser";
+open(my $outfh, '>', $outfile) or die "could not open output file $outfile";
 
 my $copymode              = 0;
 my $brace_indent          = 0;