Exclude flexparser 0.4 as workaround for IDAES/idaes-pse#1524

[lbianchi-lbl]

Summary/Motivation:

• Work around failures due to CI failures due to TypeError: cannot inherit frozen dataclass from a non-frozen one IDAES/idaes-pse#1524 while the issue is dealt with upstream

Changes proposed in this PR:

• Add requirement to exclude flexparser 0.4

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[adam-a-a]

Approving out of anticipation of checks passing

[lbianchi-lbl]

Since the failure would occur when idaes get-extensions is called, and the checks are all currently past that stage, it's safe to merge this in even before the rest of the checks have completed.

[lbianchi-lbl]

This change should ideally be reverted as the issue has been fixed upstream with Pint 0.24.4.