[IMP] web: fix typo in datepicker

Before this commit the sentence was a bit weird as a date is not on the future but in the future. This commit resolves this.

closes odoo/odoo#45548

X-original-commit: b335c33655a707f71fbc01929f5eea2e659e7215
Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>