using utf8 allows $_ to be declared with 'my'

[D1CED]

Module: utf8

Description
Without to inclusion of utf8 the 'my' declaration of $_ is a compile time error.
With using utf8 this works without warning.

Steps to Reproduce

use utf8;
my $_;

Expected behavior
my $_; should be a compile time error regardless of used modules/pragmatas.

Perl configuration

Summary of my perl5 (revision 5 version 32 subversion 0) configuration:
   
  Platform:
    osname=linux
    osvers=5.7.8-arch1-1
    archname=x86_64-linux-thread-multi
    uname='archlinux'
    config_args='-des -Dusethreads -Duseshrplib -Doptimize=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -Dprefix=/usr -Dvendorprefix=/usr -Dprivlib=/usr/share/perl5/core_perl -Darchlib=/usr/lib/perl5/5.32/core_perl -Dsitelib=/usr/share/perl5/site_perl -Dsitearch=/usr/lib/perl5/5.32/site_perl -Dvendorlib=/usr/share/perl5/vendor_perl -Dvendorarch=/usr/lib/perl5/5.32/vendor_perl -Dscriptdir=/usr/bin/core_perl -Dsitescript=/usr/bin/site_perl -Dvendorscript=/usr/bin/vendor_perl -Dinc_version_list=none -Dman1ext=1perl -Dman3ext=3perl -Dcccdlflags='-fPIC' -Dlddlflags=-shared -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -Dldflags=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -Dmyuname=archlinux -Dmyhostname=archlinux -Dcf_time=Thu Sep 17 09:12:52 PM UTC 2020'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=define
    usemultiplicity=define
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='cc'
    ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-march=x86-64 -mtune=generic -O2 -pipe -fno-plt'
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='10.2.0'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags ='-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include-fixed /usr/lib /lib/../lib /usr/lib/../lib /lib /lib64 /usr/lib64
    libs=-lpthread -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.32.so
    so=so
    useshrplib=true
    libperl=libperl.so
    gnulibc_version='2.32'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/5.32/core_perl/CORE'
    cccdlflags='-fPIC'
    lddlflags='-shared -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -L/usr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_TIMES
    MULTIPLICITY
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_IMPLICIT_CONTEXT
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_ITHREADS
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
    USE_REENTRANT_API
    USE_THREAD_SAFE_LOCALE
  Built under linux
  Compiled at Sep 17 2020 21:12:52
  %ENV:
    PERL5LIB="/home/me/perl5/lib/perl5"
    PERL_LOCAL_LIB_ROOT="/home/me/perl5"
    PERL_MB_OPT="--install_base "/home/me/perl5""
    PERL_MM_OPT="INSTALL_BASE=/home/me/perl5"
  @INC:
    /home/me/perl5/lib/perl5/5.32.0/x86_64-linux-thread-multi
    /home/me/perl5/lib/perl5/5.32.0
    /home/me/perl5/lib/perl5/x86_64-linux-thread-multi
    /home/me/perl5/lib/perl5
    /usr/lib/perl5/5.32/site_perl
    /usr/share/perl5/site_perl
    /usr/lib/perl5/5.32/vendor_perl
    /usr/share/perl5/vendor_perl
    /usr/lib/perl5/5.32/core_perl
    /usr/share/perl5/core_perl