test(styles): update button styles for test pages (#29931)

Issue number: internal

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->

## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

Test styles causes native buttons to have [certain
styling](https://github.com/ionic-team/ionic-framework/blob/main/core/scripts/testing/styles.css#L52-L64).
This was done to spruce up the buttons used for testing purposes only.
However, this ended up adding styles to native buttons within Ionic
components.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- Test styles for native buttons are only applied to buttons that are
not part of a Ionic component

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!--
  If this introduces a breaking change:
1. Describe the impact and migration path for existing applications
below.
  2. Update the BREAKING.md file with the breaking change.
3. Add "BREAKING CHANGE: [...]" to the commit description when merging.
See
https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#footer
for more information.
-->


## Other information

<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

How to test:

1. Run the project locally from the `main` branch
2.
[Comment](5d208e9daa/core/src/components/searchbar/searchbar.md.scss (L91))
out `border: 0` from `.searchbar-clear-button` from the searchbar `md`
theme file (`ios` also works)
3. Navigate to the basic test page:
`/src/components/searchbar/test/basic`
4. Notice a teal border around the clear buttons
5. Checkout to this PR's branch
6. Make sure steps 2-3 are done
7. Verify that the teal border is not being applied to the clear buttons
8. Verify that only native buttons outside of the Ionic components have
a teal appearance: `/src/components/loading/test/standalone` and
`/src/components/action-sheet/test/is-open`

core/src/components/popover/test/size/index.html

@@ -16,7 +16,7 @@
       ion-app > ion-content {
         --background: #dddddd;
       }
-      ion-content button {
+      ion-content button.trigger {
         padding: 12px 16px;
       }
       .grid {
@@ -57,26 +57,30 @@
         <div class="grid">
           <div class="grid-item">
             <h2>Cover</h2>
-            <button id="cover-trigger">Trigger</button>
+            <button id="cover-trigger" class="trigger">Trigger</button>
             <ion-popover show-backdrop="false" class="cover-popover" trigger="cover-trigger" size="cover">
               <ion-content class="ion-padding"> My really really really really long content </ion-content>
             </ion-popover>
           </div>
           <div class="grid-item">
             <h2>With Event</h2>
-            <button id="event-trigger" onclick="openPopover('event-popover', event, 'false')">Trigger</button>
+            <button id="event-trigger" class="trigger" onclick="openPopover('event-popover', event, 'false')">
+              Trigger
+            </button>
           </div>
 
           <div class="grid-item">
             <h2>Auto</h2>
-            <button id="auto-trigger">Trigger</button>
+            <button id="auto-trigger" class="trigger">Trigger</button>
             <ion-popover show-backdrop="false" class="auto-popover" trigger="auto-trigger">
               <ion-content class="ion-padding"> My really really really really long content </ion-content>
             </ion-popover>
           </div>
           <div class="grid-item">
             <h2>No Event</h2>
-            <button id="no-event-trigger" onclick="openPopover('no-event-popover', null, 'true')">Trigger</button>
+            <button id="no-event-trigger" class="trigger" onclick="openPopover('no-event-popover', null, 'true')">
+              Trigger
+            </button>
           </div>
         </div>
       </ion-content>