chore(build): fix implicit narrowing warning by making it explicit

Exact accuracy isn't needed for the normalized value, being off by one part per
quadrillion is ok.

Fix #6000

src/widget/tool/identicon.cpp

@@ -109,7 +109,7 @@ float Identicon::bytesToColor(QByteArray bytes)
 
     // normalize to 0.0 ... 1.0
     return (static_cast<float>(hue))
-           / (((static_cast<uint64_t>(1)) << (8 * IDENTICON_COLOR_BYTES)) - 1);
+           / (static_cast<float>(((static_cast<uint64_t>(1)) << (8 * IDENTICON_COLOR_BYTES)) - 1));
 }
 
 /**