fix(PollingBackend): increase poll interval on repeated network errors

When returning to a backgrounded tab, `visibilitychange` resets the fetch
interval to the minimum (300ms). Network errors never called
`increaseRefetchTimer()`, so the aggressive rate persisted indefinitely
while offline, causing ~3 sync requests per second.

Signed-off-by: Jonas <jonas@freesources.org>

Author: mejo-

src/services/PollingBackend.ts

@@ -179,6 +179,7 @@ class PollingBackend {
 	}) {
 		if (!e.response || e.code === 'ECONNABORTED') {
 			if (this.#fetchRetryCounter++ >= MAX_RETRY_FETCH_COUNT) {
+				this.increaseRefetchTimer()
 				logger.error(
 					'[PollingBackend:fetchSteps] Network error when fetching steps, emitting CONNECTION_FAILED',
 				)