*/*: Add := to virtual/zlib deps

Add := to virtual/zlib deps, part 1

Done via:

```
git grep -l virtual/zlib$ | xargs sed -i -e 's@virtual/zlib$@&:=@'
```

Add := to virtual/zlib deps

Done via:

```
git grep -l 'virtual/zlib ' |
  xargs sed -i -e 's@virtual/zlib @virtual/zlib:= @g'
```

Unify virtual/zlib:0= to virtual/zlib:=

Done via:

```
git grep -l 'virtual/zlib:0=' |
  xargs sed -i -e 's@virtual/zlib:0=@virtual/zlib:=@g'
```

Add := to virtual/zlib deps, part 3

Done via:

```
git grep -l 'virtual/zlib:0' |
  xargs sed -i -e 's@virtual/zlib:0@virtual/zlib:=@g'
git grep -l 'virtual/zlib:=/' |
  xargs sed -i -e 's@virtual/zlib:=/@virtual/zlib:0/@g'
```

Add := to virtual/zlib deps, part 4

Done via:

```
git grep -l 'virtual/zlib\[' |
  xargs sed -i -e 's@virtual/zlib\[@virtual/zlib:=\[@g'
```

Use := on virtual/zlib deps, part 5

Done via:

```
git grep -l 'virtual/zlib-' |
  xargs sed -i -r -e 's@virtual/zlib-[0-9.]*(-r[0-9]*)?@&:=@g'
git grep -l 'virtual/zlib-' | xargs sed -i -e 's@:=:=@:=@g'
pkgcheck scan --commits \
  -c SourcingCheck,VisibilityCheck,DependencyCheck --exit error
```

Use := on virtual/zlib deps, part 6

Done via:

```
git grep -l 'virtual/zlib"' | xargs sed -i -e 's@virtual/zlib"@virtual/zlib:="@'
```

Signed-off-by: Paul Zander <negril.nx+gentoo@gmail.com>

media-sound/spot/spot-0.4.0-r2.ebuild

@@ -396,7 +396,7 @@ DEPEND="
 		>=gui-libs/libadwaita-1.3.3:1
 		>=media-libs/alsa-lib-1.2.9
 		>=media-libs/libpulse-15.0[glib]
-		virtual/zlib
+		virtual/zlib:=
 		x11-libs/cairo
 		x11-libs/gdk-pixbuf:2
 		x11-libs/pango