CAMEL-23703: camel-launcher - actually run brew install/uninstall in POSIX validator

The Homebrew validator prefixed the install and uninstall commands with
`export HOME=... HOMEBREW_NO_AUTO_UPDATE=1 brew ...`. With the `export`
keyword the shell treats `brew`, its subcommand, the formula path and
`--force` as variable names to export rather than a command to run, so on a
runner where brew is present the install/uninstall steps were silent no-ops
and the validator passed without ever exercising an install.

Drop `export` so the assignments become command-prefix environment for brew
(the same form the style/audit steps already use), letting the validator fail
when an install actually breaks.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ammachado

dsl/camel-jbang/camel-launcher/src/jreleaser/bin/camel-validate.sh

@@ -162,7 +162,7 @@ validate_homebrew() {
     mkdir -p "$BREW_HOME"
     local brew_output=""
     brew_output=$(cd "$MODULE_DIR" && \
-        export HOME="$BREW_HOME" \
+        HOME="$BREW_HOME" \
         HOMEBREW_NO_AUTO_UPDATE=1 \
         brew install "$formula_file" --force 2>&1 || true)
 
@@ -207,7 +207,7 @@ validate_homebrew() {
     if command -v brew >/dev/null 2>&1; then
         local brew_uninst_output=""
         brew_uninst_output=$(cd "$MODULE_DIR" && \
-            export HOME="$BREW_HOME" \
+            HOME="$BREW_HOME" \
             HOMEBREW_NO_AUTO_UPDATE=1 \
             brew uninstall "$fmla" --force 2>&1 || true)
         echo "INFO: homebrew uninstall output:"