Harden go.mod loop against newline-containing paths in validate-go-version workflow

[Copilot]

Addresses review comment r3503331591 on PR #8906: the for f in $(find ...) loop over go.mod files breaks if any matched path contains whitespace or a newline.

Change

• Replace the word-splitting for loop with a null-delimited find -print0 piped into while IFS= read -r -d '' in .github/workflows/validate-go-version.yml.

while IFS= read -r -d '' f; do
  VERSION=$(grep -m1 '^go ' "$f" | awk '{print $2}')
  ...
done < <(find cli/azd -name 'go.mod' -print0)

Scope is limited to the go.mod loop called out in the linked comment; the other loops are left unchanged.