sysutils/screen: Bump PORTREVISION to chase src 21817992b331
21817992b331 in FreeBSD/main installed ncurses 6.5 into 15-CURRENT.
This causes screen to display errors about duplicate entries in
termcap/terminfo. A rebuild of screen fixes the problem.
The errors are:
Name collision 'cdc456tst' between
cdc456tst
and cdc456tst
Cannot remove alias 'cdc456tst'
Name collision 'tab132w' between
tab132w
and tab132w
Cannot remove alias 'tab132w'
And many more errors like the above.