Prevent using authTokenSyncURL if the string begins with a double slash

[hsubox76]

Additional fix to #8056 to prevent the string beginning with a double slash.

[changeset-bot]

🦋 Changeset detected

Latest commit: af52435

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@firebase/auth	Patch
@firebase/auth-compat	Patch
firebase	Patch

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[google-oss-bot]

Size Report ¹

Affected Products

• @firebase/auth

  Type	Base (2b22838)	Merge (a00c3e9)	Diff
  browser	177 kB	177 kB	+4 B (+0.0%)
  esm5	231 kB	231 kB	+4 B (+0.0%)
  module	177 kB	177 kB	+4 B (+0.0%)

• @firebase/auth/internal

  Type	Base (2b22838)	Merge (a00c3e9)	Diff
  browser	188 kB	188 kB	+4 B (+0.0%)
  esm5	244 kB	244 kB	+4 B (+0.0%)
  module	188 kB	188 kB	+4 B (+0.0%)

• bundle

  Type	Base (2b22838)	Merge (a00c3e9)	Diff
  auth (GoogleFBTwitterGitHubPopup)	101 kB	101 kB	+4 B (+0.0%)

• firebase

  Type	Base (2b22838)	Merge (a00c3e9)	Diff
  firebase-auth.js	147 kB	147 kB	+4 B (+0.0%)

Test Logs

• Base (2b22838): https://github.com/firebase/firebase-js-sdk/actions/runs/8209897559
• Merge (a00c3e9): https://github.com/firebase/firebase-js-sdk/actions/runs/8209996094

1. https://storage.googleapis.com/firebase-sdk-metric-reports/Bo01riETTg.html

[google-oss-bot]

Size Analysis Report ¹

Affected Products

• @firebase/auth

  • getAuth

    Size

    Type	Base (2b22838)	Merge (a00c3e9)	Diff
    size	72.4 kB	72.4 kB	+4 B (+0.0%)
    size-with-ext-deps	100 kB	100 kB	+4 B (+0.0%)

Test Logs

• Base (2b22838): https://github.com/firebase/firebase-js-sdk/actions/runs/8209897559
• Merge (a00c3e9): https://github.com/firebase/firebase-js-sdk/actions/runs/8209996094

1. https://storage.googleapis.com/firebase-sdk-metric-reports/IICpb7QsUY.html