Bug 40950: Add 'falsy' programming idiom to codespell dictionary

The term 'falsy' is a standard JavaScript idiom referring to values
that evaluate to false in boolean contexts (false, 0, '', null,
undefined, NaN). This is widely used in modern JavaScript and is
part of the official ECMAScript specification terminology. I also
believe it is relevant for Perl.

Codespell currently flags 'falsy' as a misspelling, but this is
incorrect as it's legitimate technical terminology used throughout
our JavaScript codebase and documentation.

Changes:
- Add 'falsy' to codespell exceptions/dictionary
- Allows proper use of JavaScript terminology in code and comments

Test plan:
1. Apply patch
2. Run codespell on files containing 'falsy'
=> SUCCESS: No longer flagged as misspelling
3. Verify 'falsy' usage in JavaScript context works correctly
4. Sign off :-D

Signed-off-by: Tomás Cohen Arazi <tomascohen@theke.io>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

.codespell-ignore

@@ -17,3 +17,4 @@ sav
 theses
 rouge
 connexion
+falsy

t/cypress/component/ShowElement_spec.ts

@@ -36,7 +36,7 @@ describe("ShowElement", () => {
         cy.get("label").contains("Name");
         cy.get("span").contains(resource.name);
     });
-    it("should hide that property if the hidden attribute is set and false", () => {
+    it("should hide that property if the hidden attribute is set and falsy", () => {
         cy.mount(ShowElement, {
             props: {
                 resource,