[Fix] Fixed typo in loop condition for testing model.

[jingt2ch]

When I ran tools/test.py, only one of the images in data_source was used.

Motivation

I want to evaluate my model using utils/collect.py.

Modification

Fix if statement condition in mmselfsup/utils/collect.py.

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• CLA has been signed and all committers have signed the CLA in this PR.

[tonysy]

Hi, thanks for your contribution first. Would you like to provide a test case(like bash command) to help us understand this bug?