./src/ImathTest/testMatrix.cpp:116: void testMatrix(): Assertion `m3 == m2' failed.

It seems like `i386` issues are back again in codebase. The package is failing the unit test suite on i386 arch on Debian buildds:

* https://buildd.debian.org/status/fetch.php?pkg=imath&arch=i386&ver=3.1.3-5&stamp=1638265766&raw=0

```
18: Test command: /<>/build/bin/ImathTest "testMatrix"
18: Test timeout computed to be: 1500
9: rounding normalized numbers to 1-bit precision
9: max error = 0.249634
9: max expected error = 0.249999
9: ok
9:
18: Testing functions in ImathMatrix.h
18: Imath::M22f constructors and equality operators
18: M22d constructors and equality operators
18: M22f inversion operators
18: ImathTest: ./src/ImathTest/testMatrix.cpp:116: void testMatrix(): Assertion `m3 == m2' failed.
15/38 Test #18: Imath.testMatrix ........................Subprocess aborted***Exception: 0.00 sec
Testing functions in ImathMatrix.h
Imath::M22f constructors and equality operators
M22d constructors and equality operators
M22f inversion operators
ImathTest: ./src/ImathTest/testMatrix.cpp:116: void testMatrix(): Assertion `m3 == m2' failed.
```

Start with src/ImathTest/testMatrix.cpp at line 116 and reproduce Imath.testMatrix on Debian i386, using the linked buildd failure as the reference. Trace the M22f inversion and equality checks around the assertion, then confirm the test suite passes on i386 and does not regress on other architectures.

Written by the indexing model from the issue text.