ci: shellcheck SC1007 in flashpaste-logs.sh

`CYN= YEL= MAG= DIM= OFF= BOLD=` (with spaces between bare `=`) reads
to shellcheck as five env-prefixed commands rather than empty-string
assignments. The non-TTY branch was intentionally clearing all six
color variables; rewrite as `CYN='' YEL='' ...` so the intent matches
the syntax.

Pure CI fix on top of v1.23 — no behavior change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: NagyVikt

bin/flashpaste-logs.sh

@@ -27,7 +27,7 @@ set -u
 if [ -t 1 ]; then
   CYN=$'\e[36m' YEL=$'\e[33m' MAG=$'\e[35m' DIM=$'\e[2m' OFF=$'\e[0m' BOLD=$'\e[1m'
 else
-  CYN= YEL= MAG= DIM= OFF= BOLD=
+  CYN='' YEL='' MAG='' DIM='' OFF='' BOLD=''
 fi
 
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